GraphQL

How to Leverage Apollo Client Fetch Policies Like the Pros

Published May 17, 2024

Updated May 17, 2024

7 min read

Apollo Client provides a rich ecosystem and cache for interfacing with your GraphQL APIs. You write your query and leverage the useQuery hook to fetch your data. It provides you with some state context and eventually resolves your query. That data is stored in a local, normalized, in-memory cache, which allows Apollo Client to respond to most previously run requests near instantaneously. This has huge benefits for client performance and the feel of your apps. However, sometimes Apollo's default doesn't match the user experience you want to provide. They provide fetch policies to allow you to control this behavior on each query you execute. In this article, we'll explore the different fetch policies and how you should leverage them in your application.

`cache-first`

This is the default for Apollo Client. Apollo will execute your query against the cache. If the cache can fully fulfill the request, then that's it, and we return to the client. If it can only partially match your request or cannot find any of the related data, the query will be run against your GraphQL server. The response is cached for the next query and returned to the handler.

This method prioritizes minimizing the number of requests sent to your server. However, it has an adverse effect on data that changes regularly. Think of your social media feeds - they typically contain constantly changing information as new posts are generated. Or a real-time dashboard app tracking data as it moves through a system. cache-first is probably not the best policy for these use cases as you won't fetch the latest data from the upstream source. You can lower the cache time of items for the dashboard to avoid the staleness issue and still minimize the requests being made, but this problem will persist for social media feeds.

The cache-first policy should be considered for data that does not change often in your system or data that the current user fully controls. Data that doesn't change often is easily cached, and that's a recommended pattern. For data that the user controls, we need to consider how that data changes. If only the current user can change it, we have 2 options: Return the updated data in the response of any mutation which is used to update the cache Use cache invalidation methods like refetchQueries or onQueryUpdated These methods will ensure that our cache stays in sync with our server allowing the policy to work optimally. However, if other users in the system can make changes that impact the current user's view, then we can not invalidate the cache properly using these strategies which makes this policy unideal.

`network-only`

This policy skips the cache lookup and goes to the server to fetch the results. The results are stored in the cache for other operations to leverage. Going back to the example I gave in my explanation cache-first of a social media feed, the network-only policy would be a great way to implement the feed itself as it's ever-changing, and we'll likely even want to poll for changes every 10s or so. The following is an example of what this component could look like:

import { gql, useQuery } from '@apollo/client';

const GET_FEED = gql`
  query GetFeed {
    feed {
      nodes {
        id
        post
        createdAt
        author {
          id
          # ...
        }
        interactions {
          likes {
            totalCount
          }
          reposts {
            totalCount
          }
        }
      }
      paginationInfo {
        hasNextPage
        nextCursor
      }
    }
  }
`;

export default function SocialFeed() {
  const { loading, error, data } = useQuery(GET_FEED, {
    fetchPolicy: 'network-only', // only fetch from our GraphQL server
    pollInterval: 10 * 1000, // refetch the feed every 10 seconds
  });

  if (loading) return 'Loading...';
  if (error) return `Error! ${error.message}`;

  const { feed } = data;
  const { nodes: posts, paginationInfo } = feed;
  const { hasNextPage, nextCursor } = paginationInfo;

  return (
    <>
      <Feed posts={posts} />
      {hasNextPage && (<GetMorePosts cursor={nextCursor} />)}
    </>
  );
}

Whenever this SocialFeed component is rendered, we always fetch the latest results from the GraphQL server ensuring we're looking at the current data. The results are put in the cache which we can leverage in some children components.

`cache-only`

cache-only only checks the cache for the requested data and never hits the server. It throws an error if the specified cache items cannot be found. At first glance, this cache policy may seem unhelpful because it's unclear if our cache is seeded with our data. However, in combination with the network-only policy above, this policy becomes helpful. This policy is meant for components down tree from network-only level query. This method is for you if you're a fan of React components' compatibility. We can modify the return of our previous example to be as follows:

return (
    <>
      {posts.map(post => (
        <Post key={post.id} postId={post.id} />
      ))}
      {hasNextPage && (<GetMorePosts cursor={nextCursor} />)}
    </>
  )

Notice we're not passing the full post object as a prop. This simplifies our Post component types and makes later refactors easier. The Post would like like the following:

export const POST_FRAGMENT = gql`
  fragment PostFragment on Post {
    id
    post
    createdAt
    author {
      id
      # ...
    }
    interactions {
      likes {
        totalCount
      }
      reposts {
        totalCount
      }
    }
  }
`;

const GET_POST = gql`
  query GetPost($postId: ID!) {
    post(id: $postId) {
      ...PostFragment
    }
  }
`;

export function Post({ postId }) {
  const { data } = useQuery(GET_POST, {
    variables: { postId },
    fetchPolicy: 'cache-only',
  });

  const { post } = data;

  return (
    <div>
      <p>{post.post}</p>
      <p>{post.interactions.likes.totalCount} likes</p>
      <p>{post.interactions.reposts.totalCount} reposts</p>
    </div>
  )
}

In this query, we're grabbing the data directly from our cache every time because our top-level query should have fetched it. Now, a small bug here makes maintainability a bit harder. Our top-level GetFeed query doesn't guarantee fetching the same fields. Notice how our Post component exports a fragment. Fragments are a feature Apollo supports to share query elements across operations. In our SocialFeed component, we can change our query to be:

const GET_FEED = gql`
  query GetFeed {
    feed {
      nodes {
        …PostFragment
      }
      paginationInfo {
        hasNextPage
        nextCursor
      }
    }
  }
`;

Now, as we change our Post to use new fields and display different data, the refactoring is restricted to just that component, and the upstream components will detect the changes and handle them for us making our codebase more maintainable. Because the upstream component is always fetching from the network, we can trust that the cache will have our data, making this component safe to render. With these examples, though, our users will likely have to see a loading spinner or state on every render unless we add some server rendering.

`cache-and-network`

This is where cache-and-network comes to play. With this policy, Apollo Client will run your query against your cache and your GraphQL server. This further simplifies our example above if we want to provide the last fetched results to the user but then update the feed immediately upon gathering the latest data. This is similar to what X/Twitter does when you reload the app. You'll see the last value that was in the cache then it'll render the network values when ready. This can cause a jarring user experience though, if the data is changing a lot over time, so I recommend using this methodology sparsely. However, if you wanted to update our existing example, we'd just change our SocialFeed component to use this policy, and that'll keep our client and server better in sync while still enabling 10s polling.

`no-cache`

This policy is very similar to the network-only policy, except it bypasses the local cache entirely. In our previous example, we wrote engagement as a sub-selector on a Post and stored fields there. These metrics can change in real time pretty drastically. Chat features, reactions, viewership numbers, etc., are all types of data that may change in real time. The no-cache policy is good when this type of data is active, such as during a live stream or within the first few hours of a post going out. You may typically want to use the cache-and-network policy eventually but during that active period, you'll probably want to use no-cache so your consumers can trust your data. I'd probably recommend changing your server to split these queries and run different policies for the operations for performance reasons. I haven't mentioned this yet, but you can make the fetch policy on a query dynamic, meaning you combine these different policies' pending states. This could look like the following:

import { gql, useQuery } from '@apollo/client';

const GET_CHAT = gql`
  query GetChat {
    chat {
      id
      messages {
        id
        content
        author {
          id
          name
        }
      }
    }
  }
`;

export default function ChatFeed({ isLive }: { isLive: boolean }) {
  const { loading, error, data } = useQuery(GET_CHAT, {
    fetchPolicy: isLive ? 'no-cache' : 'cache-and-network', // only cache if we're not live
    pollInterval: 10 * 1000, // refetch the feed every 10 seconds
  });

  if (loading) return 'Loading...';
  if (error) return `Error! ${error.message}`;

  const { chat } = data;
  const { messages } = chat;

  return (
    <Chat messages={messages} />
  );
}

We pass whether the event is live to the component that then leverages that info to determine if we should cache or not when fetching the chat. That being said, we should consider using subscription operations for this type of feature as well, but that's an exercise for another blog post.

`standby`

This is the most uncommon fetch policy, but has a lot of use. This option runs like a cache-first query when it executes. However, by default, this query does not run and is treated like a "skip" until it is manually triggered by a refetch or updateQueries caller. You can achieve similar results by leveraging the useLazyQuery operator, but this maintains the same behavior as other useQuery operators so you'll have more consistency among your components. This method is primarily used for operations pending other queries to finish or when you want to trigger the caller on a mutation. Think about a dashboard with many filters that need to be applied before your query executes. The standby fetch policy can wait until the user hits the Apply or Submit button to execute the operation then calls a await client.refetchQueries({ include: ["DashboardQuery"] }), which will then allow your component to pull in the parameters for your operation and execute it. Again, you could achieve this with useLazyQuery so it's really up to you and your team how you want to approach this problem. To avoid learning 2 ways, though, I recommend picking just one path.

Conclusion

Apollo Client's fetch policies are a versatile and helpful tool for managing your application data and keeping it in sync with your GraphQL server. In general, you should use the defaults provided by the library, but think about the user experience you want to provide. This will help you determine which policy best meets your needs. Leveraging tools like fragments will enable you to manage your application and use composable patterns more effectively.

With the rise of React Server Components and other similar patterns, you'll need to be wary of how that impacts your Apollo Client strategy. However, if you're on a legacy application that leverages traditional SSR patterns, Apollo allows you to pre-render queries on the server and their related cache. When you combine these technologies, you'll find that your apps perform great, and your users will be delighted.

This Dot is a consultancy dedicated to guiding companies through their modernization and digital transformation journeys. Specializing in replatforming, modernizing, and launching new initiatives, we stand out by taking true ownership of your engineering projects.

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About the author(s)

Dustin Goodman
Engineering Manager with a passion for web and application development. Speaker and writer on work experiences and software development. Dog dad and musician fueled by coffee.
@dustinsgoodman @dustinsgoodman

How to Resolve Nested Queries in Apollo Server

When working with relational data, there will be times when you will need to access information within nested queries. But how would this work within the context of Apollo Server? In this article, we will take a look at a few code examples that explore different solutions on how to resolve nested queries in Apollo Server. I have included all code examples in CodeSandbox if you are interested in trying them out on your own. Prerequisites This article assumes that you have a basic knowledge of GraphQL terminology. Table of Contents - How to resolve nested queries: An approach using resolvers and the filter method - A refactored approach using Data Loaders and Data Sources - What are Data Loaders - How to setup a Data Source - Setting up our schemas and resolvers - Resolving nested queries when microservices are involved - Conclusion How to resolve nested queries: An approach using resolvers and the filter method In this first example, we are going to be working with two data structures called musicBrands and musicAccessories. musicBrands is a collection of entities consisting of id and name. musicAccessories is a collection of entities consisting of the product name, price, id and an associated brandId. You can think of the brandId as a foreign key that connects the two database tables. We also need to set up the schemas for the brands and accessories. ` The next step is to set up a resolver for our Query to return all of the music accessories. ` When we run the following query and start the server, we will see this JSON output: ` ` As you can see, we are getting back the value of null for the brands field. This is because we haven't set up that relationship yet in the resolvers. Inside our resolver, we are going to create another query for the MusicAccessories and have the value for the brands key be a filtered array of results for each brand. ` When we run the query, this will be the final result: ` ` This single query makes it easy to access the data we need on the client side as compared to the REST API approach. If this were a REST API, then we would be dealing with multiple API calls and a Promise.all which could get a little messy. You can find the entire code in this CodeSandbox example. A refactored approach using Data Loaders and Data Sources Even though our first approach does solve the issue of resolving nested queries, we still have an issue fetching the same data repeatedly. Let’s look at this example query: ` If we take a look at the results, we are making additional queries for the brand each time we request the information. This leads to the N+1 problem in our current implementation. We can solve this issue by using Data Loaders and Data Sources. What are Data Loaders Data Loaders are used to batch and cache fetch requests. This allows us to fetch the same data and work with cached results, and reduce the number of API calls we have to make. To learn more about Data Loaders in GraphQL, please read this helpful article. How to setup a Data Source In this example, we will be using the following packages: - apollo-datasource - apollo-server-caching - dataloader We first need to create a BrandAccessoryDataSource class which will simulate the fetching of our data. ` We will then set up a constructor with a custom Dataloader. ` Right below our constructor, we will set up the context and cache. ` We then want to set up the error handling and cache keys for both the accessories and brands. To learn more about how caching works with GraphQL, please read through this article. ` Next, we are going to set up an asynchronous function called get which takes in an id. The goal of this function is to first check if there is anything in the cached results and if so return those cached results. Otherwise, we will set that data to the cache and return it. We will set the ttl(Time to Live in cache) value to 15 seconds. ` Below the get function, we will create another asynchronous function called getByBrand which takes in a brand. This function will have a similar setup to the get function but will filter out the data by brand. ` Setting up our schemas and resolvers The last part of this refactored example includes modifying the resolvers. We first need to add an accessory key to our Query schema. ` Inside the resolver, we will add the accessories key with a value for the function that returns the data source we created earlier. ` We also need to refactor our Brand resolver to include the data source we set up earlier. ` Lastly, we need to modify our ApolloServer object to include the BrandAccessoryDataSource. ` Here is the entire CodeSandbox example. When the server starts up, click on the Query your server button and run the following query: ` Resolving nested queries when microservices are involved Microservices is a type of architecture that will split up your software into smaller independent services. All of these smaller services can interact with a single API data layer. In this case, this data layer would be GraphQL. The client will interact directly with this data layer, and will consume API data from a single entry point. You would similarly resolve your nested queries as before because, at the end of the day, there are just functions. But now, this single API layer will reduce the number of requests made by the client because only the data layer will be called. This simplifies the data fetching experience on the client side. Conclusion In this article, we looked at a few code examples that explored different solutions on how to resolve nested queries in Apollo Server. The first approach involved creating custom resolvers and then using the filter method to filter out music accessories by brand. We then refactored that example to use a custom DataLoader and Data Source to fix the "N+1 problem". Lastly, we briefly touched on how to approach this solution if microservices were involved. If you want to get started with Apollo Server and build your own nested queries and resolvers using these patterns, check out our serverless-apollo-contentful starter kit!...

May 17, 2023

6 mins

GraphQL

Introducing the New Serverless, GraphQL, Apollo Server, and Contentful Starter kit

Introducing the new Serverless, GraphQL, Apollo Server, and Contentful Starter kit The team at This Dot Labs has released a brand new starter kit which includes the Serverless Framework, GraphQL, Apollo Server and Contentful configured and ready to go. This article will walk through how to set up the new kit, the key technologies used, and reasons why you would consider using this kit. Table of Contents - How to get started setting up the kit - Generate the project - Setup Contentful access - Setting up Docker - Starting the local server - How to Create the Technology Model in Contentful - How to seed the database with demo data - How to work with the migration scripts - Technologies included in this starter kit - Why use GraphQL? - Why use Contentful? - Why use Amazon Simple Queue Service (SQS)? - Why use Apollo Server? - Why use the Serverless Framework? - Why use Redis? - Why use the Jest testing framework? - Project structure - How to deploy your application - What can this starter kit be used for? - Conclusion How to get started setting up the kit Generate the project In the command line, you will need to start the starter.dev CLI by running the npx @this-dot/create-starter command. You can then select the Serverless Framework, Apollo Server, and Contentful CMS kit and name your new project. Then you will need to cd into your new project directory and install the dependencies using the tool of your choice (npm, yarn, or pnpm). Next, you will need to Run cp .env.example .env to copy the contents of the .env.example file into the .env file. Setup Contentful access You will first need to create an account on Contentful, if you don't have one already. Once you are logged in, you will need to create a new space. From there, go to Settings -> API keys and click on the Content Management Tokens tab. Next, click on the Generate personal token button and give your token a name. Copy your new Personal Access Token, and add it to the CONTENTFUL_CONTENT_MANAGEMENT_API_TOKEN variable. Then, go to Settings -> General settings to get the CONTENTFUL_SPACE_ID. The last step is to add those CONTENTFUL_CONTENT_MANAGEMENT_API_TOKEN and CONTENTFUL_SPACE_ID values to your .env file. Setting up Docker You will first need to install Docker Desktop if you don't have it installed already. Once installed, you can start up the Docker container with the npm run infrastructure:up command. Starting the local server While the Docker container is running, open up a new tab in the terminal and run npm run dev to start the development server. Open your browser to http://localhost:3000/dev/graphql to open up Apollo server. How to Create the Technology Model in Contentful To get started with the example model, you will first need to create the model in Contentful. 1. Log into your Contentful account 2. Click on the Content Model tab 3. Click on the Design your Content Modal button if this is your first modal 4. Create a new model called Technology 5. Add three new text fields called displayName, description and url 6. Save your new model How to seed the database with demo data This starter kit comes with a seeding script that pre-populates data for the Technology Content type. In the command line, run npm run db:seed which will add three new data entries into Contentful. If you want to see the results from seeding the database, you can execute a small GraphQL query using Apollo server. First, make sure Docker, and the local server(npm run dev) are running, and then navigate to http://localhost:3000/dev/graphql. Add the following query: ` When you run the query, you should see the following output. ` How to work with the migration scripts Migrations are a way to make changes to your content models and entries. This starter kit comes with a couple of migration scripts that you can study and run to make changes to the demo Technology model. These migration scripts are located in the scripts/migration directory. To get started, you will need to first install the contentful-cli. ` You can then login to Contentful using the contentful-cli. ` You will then need to choose the Contentful space where the Technology model is located. ` If you want to modify the existing demo content type, you can run the second migration script from the starter kit. ` If you want to build out more content models using the CLI, you can study the example code in the /scripts/migrations/01-create-technology-contentType.js file. From there, you can create a new migration file, and run the above contentful space migration command. If you want to learn more about migration in Contentful, then please check out the documentation. Technologies included in this starter kit Why use GraphQL? GraphQL is a query language for your API and it makes it easy to query all of the data you need in a single request. This starter kit uses GraphQL to query the data from our Contentful space. Why use Contentful? Contentful is a headless CMS that makes it easy to create and manage structured data. We have integrated Contentful into this starter kit to make it easy for you to create new entries in the database. Why use Amazon Simple Queue Service (SQS)? Amazon Simple Queue Service (SQS) is a queuing service that allows you to decouple your components and process and store messages in a scalable way. In this starter kit, an SQS message is sent by the APIGatewayProxyHandler using the sendMessage function, which is then stored in a queue called DemoJobQueue. The SQS handler sqs-handler polls this queue, and processes any message received. ` Why use Apollo Server? Apollo Server is a production-ready GraphQL server that works with any GraphQL client, and data source. When you run npm run dev and open the browser to http://localhost:3000/dev/graphql, you will be able to start querying your Contentful data in no time. Why use the Serverless Framework? The Serverless Framework is used to help auto-scale your application by using AWS Lambda functions. In the starter kit, you will find a serverless.yml file, which acts as a configuration for the CLI and allows you to deploy your code to your chosen provider. This starter kit also includes the following plugins: - serverless-offline - allows us to deploy our application locally to speed up development cycles. - serverless-plugin-typescript - allows the use of TypeScript with zero-config. - serverless-dotenv-plugin - preloads function environment variables into the Serverless Framework. Why use Redis? Redis is an open-source in-memory data store that stores data in the server memory. This starter kit uses Redis to cache the data to reduce the API response times and rate limiting. When you make a new request, those new requests will be retrieved from the Redis cache. Why use the Jest testing framework? Jest is a popular testing framework that works well for creating unit tests. You can see some example test files under the src/schema/technology directory. You can use the npm run test command to run all of the tests. Project structure Inside the src directory, you will find the following structure: ` This given structure makes it easy to find all of the code and tests related to that specific component. This structure also follows the single responsibility principle which means that each file has a single purpose. How to deploy your application The Serverless Framework needs access to your cloud provider account so that it can create and manage resources on your behalf. You can follow the guide to get started. Steps to get started: 1. Sign up for an AWS account 2. Create an IAM User and Access Key 3. Export your AWS_ACCESS_KEY_ID & AWS_SECRET_ACCESS_KEY credentials. ` 4. Deploy your application on AWS Lambda: ` 5. To deploy a single function, run: ` To stop your Serverless application, run: ` For more information on Serverless deployment, check out this article. What can this starter kit be used for? This starter kit is very versatile, and can be used with a front-end application for a variety of situations. Here are some examples: - personal developer blog - small e-commerce application Conclusion In this article, we looked at how we can get started using the Serverless, GraphQL, Apollo Server, and Contentful Starter kit. We also looked at the different technologies used in the kit, and why they were chosen. Lastly, we looked at how to deploy our application using AWS. I hope you enjoy working with our new starter kit!...

Jun 2, 2023

7 mins

GraphQL

The Dangers of ORMs and How to Avoid Them

Background We recently engaged with a client reporting performance issues with their product. It was a legacy ASP .NET application using Entity Framework to connect to a Microsoft SQL Server database. As the title of this post and this information suggest, the misuse of this Object-Relational Mapping (ORM) tool led to these performance issues. Since our blog primarily focuses on JavaScript/TypeScript content, I will leverage TypeORM to share examples that communicate the issues we explored and their fixes, as they are common in most ORM tools. Our Example Data If you're unfamiliar with TypeORM I recommend reading their docs or our other posts on the subject. To give us a variety of data situations, we will leverage a classic e-commerce example using products, product variants, customers, orders, and order line items. Our data will be related as follows: The relationship between customers and products is one we care about, but it is optional as it could be derived from customer->order->order line item->product. The TypeORM entity code would look as follows: ` With this example set, let's explore some common misuse patterns and how to fix them. N + 1 Queries One of ORMs' superpowers is quick access to associated records. For example, we want to get a product and its variants. We have 2 options for writing this operation. The first is to join the table at query time, such as: ` Which resolves to a SQL statement like (mileage varies with the ORM you use): ` The other option is to query the product variants separately, such as: ` This example executes 2 queries. The join operation performs 1 round trip to the database at 200ms, whereas the two operations option performs 2 round trips at 100ms. Depending on the location of your database to your server, the round trip time will impact your decision here on which to use. In this example, the decision to join or not is relatively unimportant and you can implement caching to make this even faster. But let's imagine a different situation/query that we want to run. Let's say we want to fetch a set of orders for a customer and all their order items and the products associated with them. With our ORM, we may want to write the following: ` When written out like this and with our new knowledge of query times, we can see that we'll have the following performance: 100ms * 1 query for orders + 100ms * order items count + 100ms * order items' products count. In the best case, this only takes 100ms, but in the worst case, we're talking about seconds to process all the data. That's an O(1 + N + M) operation! We can eagerly fetch with joins or collection queries based on our entity keys, and our query performance becomes closer to 100ms for orders + 100ms for order line items join + 100ms for product join. In the worst case, we're looking at 300ms or O(1)! Normally, N+1 queries like this aren't so obvious as they're split into multiple helper functions. In other languages' ORMs, some accessors look like property lookups, e.g. order.orderItems. This can be achieved with TypeORM using their lazy loading feature (more below), but we don't recommend this behavior by default. Also, you need to be wary of whether your ORM can be utilized through a template/view that may be looping over entities and fetching related records. In general, if you see a record being looped over and are experiencing slowness, you should verify if you've prefetched the data to avoid N+1 operations, as they can be a major bottleneck for performance. Our above example can be optimized by doing the following: ` Here, we prefetch all the needed order items and products and then index them in a hash table/dictionary to look them up during our loops. This keeps our code with the same readability but improves the performance, as in-memory lookups are constant time and nearly instantaneous. For performance comparison, we'd need to compare it to doing the full operation in the database, but this removes the egregious N+1 operations. Eager v Lazy Loading Another ORM feature to be aware of is eager loading and lazy loading. This implementation varies greatly in different languages and ORMs, so please reference your tool's documentation to confirm its behavior. TypeORM's eager v lazy loading works as follows: - If eager loading is enabled for a field when you fetch a record, the relationship will automatically preload in memory. - If lazy loading is enabled, the relationship is not available by default, and you need to request it via a key accessor that executes a promise. - If neither is enabled, it defaults to the behavior ascribed above when we explained handling N+1 queries. Sometimes, you don't want these relationships to be preloaded as you don't use the data. This behavior should not be used unless you have a set of relations that are always loaded together. In our example, products likely will always need product variants loaded, so this is a safe eager load, but eager loading order items on orders wouldn't always be used and can be expensive. You also need to be aware of the nuances of your ORM. With our original problem, we had an operation that looked like product.productVariants.insert({ … }). If you read more on Entity Framework's handling of eager v lazy loading, you'll learn that in this example, the product variants for the product are loaded into memory first and then the insert into the database happens. Loading the product variants into memory is unnecessary. A product with 100s (if not 1000s) of variants can get especially expensive. This was the biggest offender in our client's code base, so flipping the query to include the ID in the insert operation and bypassing the relationship saved us _seconds_ in performance. Database Field Performance Issues Another issue in the project was loading records with certain data types in fields. Specifically, the text type. The text type can be used to store arbitrarily long strings like blog post content or JSON blobs in the absence of a JSON type. Most databases use a technique that stores text fields off rows, which requires a special file system lookup operation to fetch that data. This can make a typical database lookup that would take 100ms under normal conditions to take 200ms. If you combine this problem with some of the N+1 and eager loading problems we've mentioned, this can lead to seconds, if not minutes, of query slowdown. For these, you should consider not including the column by default as part of your ORM. TypeORM allows for this via their hidden columns feature. In this example, for our product description, we could change the definition to be: ` This would allow us to query products without descriptions quickly. If we needed to include the product description in an operation, we'd have to use the addSelect function to our query to include that data in our result like: ` This is an optimization you should be wary of making in existing systems but one worth considering to improve performance, especially for data reports. Alternatively, you could optimize a query using the select method to limit the fields returned to those you need. Database v. In-Memory Fetching Going back to one of our earlier examples, we wrote the following: ` This involves loading our data in memory and then using system memory to perform a group-by operation. Our database could have also returned this result grouped. We opted to perform this operation like this because it made fetching the order item IDs easier. This takes some performance challenges away from our database and puts the performance effort on our servers. Depending on your database and other system constraints, this is a trade-off, so do some benchmarking to confirm your best options here. This example is not too bad, but let's say we wanted to get all the orders for a customer with an item that cost more than $20. Your first inclination might be to use your ORM to fetch all the orders and their items and then filter that operation in memory using JavaScript's filter method. In this case, you're loading data you don't need into memory. This is a time to leverage the database more. We could write this query as follows in SQL: ` This just loads the orders that had the data that matched our condition. We could write this as: ` We constrained this to a single customer, but if it were for a set of customers, it could be significantly faster than loading all the data into memory. If our server has memory limitations, this is a good concern to be aware of when optimizing for performance. We noticed a few instances on our client's implementation where the filter operations were applied in functions that appeared to run the operation in the database but were running the operation in memory, so this was preloading more data into memory than needed on a memory-constrained server. Refer to your ORM manual to avoid this type of performance hit. Lack of Indexes The final issue we encountered was a lack of indexes on key lookups. Some ORMs do not support defining indexes in code and are manually applied to databases. These tend not to be documented, so an out-of-sync issue can happen in different environments. To avoid this challenge, we prefer ORMs that support indexes in code like TypeORM. In our last example, we filtered on the cost of an order item, but the cost field does not contain an index. This leads to a full table scan of our data collection filtered by the customer. The query cost can be very expensive if a customer has thousands of orders. Adding the index can make our query super fast, but it comes at a cost. Each new index makes writing to the database slower and can exponentially increase the size of our database needs. You should only add indexes to fields that you are querying against regularly. Again, be sure you can notate these indexes in code so they can be replicated across environments easily. In our client's system, the previous developer did not include indexes in the code, so we retroactively added the database indexes to the codebase. We recommend using your database's recommended tool for inspection to determine what indexes are in place and keep these systems in sync at all times. Conclusion ORMs can be an amazing tool to help you and your teams build applications quickly. However, they have gotchas for performance that you should be aware of and can identify while developing or during code reviews. These are some of the most common examples I could think of for best practices. When you hear the horror stories about ORMs, these are some of the challenges typically discussed. I'm sure there are more, though. What are some that you know? Let us know!...

Jul 3, 2024

8 mins

Architectural DesignDesign PatternsArchitecture

How Nuxt Studio is Redefining Developer & User Experience with Baptiste Leproux & Ferdinand Coumau

In this episode of the Modern Web Podcast, Danny Thompson sits down with Ferdinand Como and Baptiste Leproux from Nuxt Labs to uncover the story behind Nuxt Studio, a tool that's transforming how developers and non-technical users interact with Nuxt applications. Ferdinand and Baptiste share how Nuxt Studio bridges the gap between developer customization and user-friendly content management. Built to empower agencies, freelancers, and their clients, Nuxt Studio combines powerful features like live previews, Vue component integration, and schema-driven forms to make managing content seamless. The conversation also explores the broader mission of Nuxt Labs—building sustainable open-source tools that enhance developer experience and meet real-world needs. With insights into the future of Nuxt Studio and its potential to scale for larger organizations, this episode is a must-listen for anyone passionate about innovation in web development. Chapters 1. Introduction and Setting the Stage (00:00:00) 2. The Vision Behind Nuxt Studio (00:03:10) 3. Nuxt Studio’s Core Features (00:08:45) 4. Challenges in Building Nuxt Studio (00:16:20) 5. Target Audience and Use Cases (00:22:35) 6. Sustainability in Open Source (00:29:00) 7. The Future of Nuxt Studio (00:35:10) 8. Nuxt Studio’s Role in the Nuxt Ecosystem (00:42:30) 9. Closing Thoughts and What’s Next (00:48:00) 10. Sponsor Shoutout and Wrap-Up (00:53:20) Follow Baptiste Leproux and Ferdinand Coumau Baptiste Twitter: https://x.com/_larbish Ferdinand Twitter: https://x.com/CoumauFerdinand Baptiste Linkedin: https://www.linkedin.com/in/baptiste-leproux-618842b0/ Ferdinand Linkedin: https://www.linkedin.com/in/ferdinand-coumau-nuxt/ Sponsored by This Dot: thisdot.co...

Nov 20, 2024

2 mins

VueNuxtJS

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How to Leverage Apollo Client Fetch Policies Like the Pros

`cache-first`

`network-only`

`cache-only`

`cache-and-network`

`no-cache`

`standby`

Conclusion

Dustin Goodman

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