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Actions

Actions can call third party services to do things such as processing a payment with Stripe. They can be run in Convex's JavaScript environment or in Node.js. They can interact with the database indirectly by calling queries and mutations.

Example: GIPHY Action

Action names​

Actions follow the same naming rules as queries, see Query names.

The action constructor​

To declare an action in Convex you use the action constructor function. Pass it an object with a handler function, which performs the action:

convex/myFunctions.ts
TS
import { action } from "./_generated/server";

export const doSomething = action({
  handler: () => {
    // implementation goes here

    // optionally return a value
    return "success";
  },
});

Unlike a query, an action can but does not have to return a value.

Action arguments and responses​

Action arguments and responses follow the same rules as mutations:

convex/myFunctions.ts
TS
import { action } from "./_generated/server";
import { v } from "convex/values";

export const doSomething = action({
  args: { a: v.number(), b: v.number() },
  handler: (_, args) => {
    // do something with `args.a` and `args.b`

    // optionally return a value
    return "success";
  },
});

The first argument to the handler function is reserved for the action context.

Action context​

The action constructor enables interacting with the database, and other Convex features by passing an ActionCtx object to the handler function as the first argument:

convex/myFunctions.ts
TS
import { action } from "./_generated/server";
import { v } from "convex/values";

export const doSomething = action({
  args: { a: v.number(), b: v.number() },
  handler: (ctx, args) => {
    // do something with `ctx`
  },
});

Which part of that action context is used depends on what your action needs to do:

  • To read data from the database use the runQuery field, and call a query that performs the read:

    convex/myFunctions.ts
    TS
    import { action, internalQuery } from "./_generated/server";
    import { internal } from "./_generated/api";
    import { v } from "convex/values";

    export const doSomething = action({
      args: { a: v.number() },
      handler: async (ctx, args) => {
        const data = await ctx.runQuery(internal.myFunctions.readData, {
          a: args.a,
        });
        // do something with `data`
      },
    });

    export const readData = internalQuery({
      args: { a: v.number() },
      handler: async (ctx, args) => {
        // read from `ctx.db` here
      },
    });

    Here readData is an internal query because we don't want to expose it to the client directly. Actions, mutations and queries can be defined in the same file.

  • To write data to the database use the runMutation field, and call a mutation that performs the write:

    convex/myFunctions.ts
    TS
    import { v } from "convex/values";
    import { action } from "./_generated/server";
    import { internal } from "./_generated/api";

    export const doSomething = action({
      args: { a: v.number() },
      handler: async (ctx, args) => {
        const data = await ctx.runMutation(internal.myMutations.writeData, {
          a: args.a,
        });
        // do something else, optionally use `data`
      },
    });

    Use an internal mutation when you want to prevent users from calling the mutation directly.

    As with queries, it's often convenient to define actions and mutations in the same file.

  • To generate upload URLs for storing files use the storage field. Read on about File Storage.

  • To check user authentication use the auth field. Auth is propagated automatically when calling queries and mutations from the action. Read on about Authentication.

  • To schedule functions to run in the future, use the scheduler field. Read on about Scheduled Functions.

  • To search a vector index, use the vectorSearch field. Read on about Vector Search.

Dealing with circular type inference​

Working around the TypeScript error: some action implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.

When the return value of an action depends on the result of calling ctx.runQuery or ctx.runMutation, TypeScript will complain that it cannot infer the return type of the action. This is a minimal example of the issue:

convex/myFunctions.ts
// TypeScript reports an error on `myAction`
export const myAction = action({
  args: {},
  handler: async (ctx) => {
    return await ctx.runQuery(api.myFunctions.getSomething);
  },
});

export const getSomething = query({
  args: {},
  handler: () => {
    return null;
  },
});

To work around this, there are two options:

  1. Type the return value of the handler function explicitly:
    convex/myFunctions.ts
    export const myAction = action({
      args: {},
      handler: async (ctx): Promise<null> => {
        const result = await ctx.runQuery(api.myFunctions.getSomething);
        return result;
      },
    });
  2. Type the the result of the ctx.runQuery or ctx.runMutation call explicitly:
    convex/myFunctions.ts
    export const myAction = action({
      args: {},
      handler: async (ctx) => {
        const result: null = await ctx.runQuery(api.myFunctions.getSomething);
        return result;
      },
    });

TypeScript will check that the type annotation matches what the called query or mutation returns, so you don't lose any type safety.

In this trivial example the return type of the query was null. See the TypeScript page for other types which might be helpful when annotating the result.

Choosing the runtime ("use node")​

Actions can run in Convex's custom JavaScript environment or in Node.js.

By default, actions run in Convex's environment. This environment supports fetch, so actions that simply want to call a third-party API using fetch can be run in this environment:

convex/myFunctions.ts
TS
import { action } from "./_generated/server";

export const doSomething = action({
  args: {},
  handler: async () => {
    const data = await fetch("https://api.thirdpartyservice.com");
    // do something with data
  },
});

Actions running in Convex's environment are faster compared to Node.js, since they don't require extra time to start up before running your action (cold starts). They can also be defined in the same file as other Convex functions. Like queries and mutations they can import NPM packages, but not all are supported.

Actions needing unsupported NPM packages or Node.js APIs can be configured to run in Node.js by adding the "use node" directive at the top of the file. Note that other Convex functions cannot be defined in files with the "use node"; directive.

convex/myAction.ts
TS
"use node";

import { action } from "./_generated/server";
import SomeNpmPackage from "some-npm-package";

export const doSomething = action({
  args: {},
  handler: () => {
    // do something with SomeNpmPackage
  },
});

Learn more about the two Convex Runtimes.

Splitting up action code via helpers​

Just like with queries and mutations you can define and call helper

TypeScript
functions to split up the code in your actions or reuse logic across multiple Convex functions.

But note that the ActionCtx only has the auth field in common with QueryCtx and MutationCtx.

Calling actions from clients​

To call an action from React use the useAction hook along with the generated api object.

src/myApp.tsx
TS
import { useAction } from "convex/react";
import { api } from "../convex/_generated/api";

export function MyApp() {
  const performMyAction = useAction(api.myFunctions.doSomething);
  const handleClick = () => {
    performMyAction({ a: 1 });
  };
  // pass `handleClick` to a button
  // ...
}

Unlike mutations, actions from a single client are parallelized. Each action will be executed as soon as it reaches the server (even if other actions and mutations from the same client are running). If your app relies on actions running after other actions or mutations, make sure to only trigger the action after the relevant previous function completes.

Note: In most cases calling an action directly from a client is an anti-pattern. Instead, have the client call a mutation which captures the user intent by writing into the database and then schedules an action:

convex/myFunctions.ts
TS
import { v } from "convex/values";
import { internal } from "./_generated/api";
import { internalAction, mutation } from "./_generated/server";

export const mutationThatSchedulesAction = mutation({
  args: { text: v.string() },
  handler: async (ctx, { text }) => {
    const taskId = await ctx.db.insert("tasks", { text });
    await ctx.scheduler.runAfter(0, internal.myFunctions.actionThatCallsAPI, {
      taskId,
      text,
    });
  },
});

export const actionThatCallsAPI = internalAction({
  args: { taskId: v.id("tasks"), text: v.string() },
  handler: (_, args): void => {
    // do something with `taskId` and `text`, like call an API
    // then run another mutation to store the result
  },
});

This way the mutation can enforce invariants, such as preventing the user from executing the same action twice.

Limits​

Actions time out after 10 minutes. Node.js and Convex runtime have 512MB and 64MB memory limit respectively. Please contact us if you have a use case that requires configuring higher limits.

Actions can do up to 1000 concurrent operations, such as executing queries, mutations or performing fetch requests.

For information on other limits, see here.

Error handling​

Unlike queries and mutations, actions may have side-effects and therefore can't be automatically retried by Convex when errors occur. For example, say your action calls Stripe to send a customer invoice. If the HTTP request fails, Convex has no way of knowing if the invoice was already sent. Like in normal backend code, it is the responsibility of the caller to handle errors raised by actions and retry the action call if appropriate.

Dangling promises​

Make sure to await all promises created within an action. Async tasks still running when the function returns might or might not complete. In addition, since the Node.js execution environment might be reused between action calls, dangling promises might result in errors in subsequent action invocations.

Best practices​

await ctx.runAction should only be used for crossing JS runtimes​

Why? await ctx.runAction incurs to overhead of another Convex server function. It counts as an extra function call, it allocates it's own system resources, and while you're awaiting this call the parent action call is frozen holding all it's resources. If you pile enough of these calls on top of each other, your app may slow down significantly.

Fix: The reason this api exists is to let you run code in the Node.js environment. If you want to call an action from another action that's in the same runtime, which is the normal case, the best way to do this is to pull the code you want to call into a TypeScript helper function and call the helper instead.

Avoid await ctx.runMutation / await ctx.runQuery​

// ❌
const foo = await ctx.runQuery(...)
const bar = await ctx.runQuery(...)

// ✅
const fooAndBar = await ctx.runQuery(...)

Why? Multiple runQuery / runMutations execute in separate transactions and aren’t guaranteed to be consistent with each other (e.g. foo and bar could read the same document and return two different results), while a single runQuery / runMutation will always be consistent. Additionally, you’re paying for multiple function calls when you don’t have to.

Fix: Make a new internal query / mutation that does both things. Refactoring the code for the two functions into helpers will make it easy to create a new internal function that does both things while still keeping around the original functions. Potentially try and refactor your action code to “batch” all the database access.

Caveats: Separate runQuery / runMutation calls are valid when intentionally trying to process more data than fits in a single transaction (e.g. running a migration, doing a live aggregate).