Convex guidelines

---
trigger: model_decision
description: Convex guidelines
---

# Convex guidelines
## Function guidelines
### New function syntax
- ALWAYS use the new function syntax for Convex functions. For example:
```typescript
import { query } from "./_generated/server";
import { v } from "convex/values";
export const f = query({
    args: {},
    returns: v.null(),
    handler: async (ctx, args) => {
    // Function body
    },
});
```

### Http endpoint syntax
- HTTP endpoints are defined in `convex/http.ts` and require an `httpAction` decorator. For example:
```typescript
import { httpRouter } from "convex/server";
import { httpAction } from "./_generated/server";
const http = httpRouter();
http.route({
    path: "/echo",
    method: "POST",
    handler: httpAction(async (ctx, req) => {
    const body = await req.bytes();
    return new Response(body, { status: 200 });
    }),
});
```
- HTTP endpoints are always registered at the exact path you specify in the `path` field. For example, if you specify `/api/someRoute`, the endpoint will be registered at `/api/someRoute`.

### Validators
- Below is an example of an array validator:
```typescript
import { mutation } from "./_generated/server";
import { v } from "convex/values";

export default mutation({
args: {
    simpleArray: v.array(v.union(v.string(), v.number())),
},
handler: async (ctx, args) => {
    //...
},
});
```
- Below is an example of a schema with validators that codify a discriminated union type:
```typescript
import { defineSchema, defineTable } from "convex/server";
import { v } from "convex/values";

export default defineSchema({
    results: defineTable(
        v.union(
            v.object({
                kind: v.literal("error"),
                errorMessage: v.string(),
            }),
            v.object({
                kind: v.literal("success"),
                value: v.number(),
            }),
        ),
    )
});
```
- Always use the `v.null()` validator when returning a null value. Below is an example query that returns a null value:
```typescript
import { query } from "./_generated/server";
import { v } from "convex/values";

export const exampleQuery = query({
  args: {},
  returns: v.null(),
  handler: async (ctx, args) => {
      console.log("This query returns a null value");
      return null;
  },
});
```
- Here are the valid Convex types along with their respective validators:
Convex Type  | TS/JS type  |  Example Usage         | Validator for argument validation and schemas  | Notes                                                                                                                                                                                                 |
| ----------- | ------------| -----------------------| -----------------------------------------------| ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Id          | string      | `doc._id`              | `v.id(tableName)`                              |                                                                                                                                                                                                       |
| Null        | null        | `null`                 | `v.null()`                                     | JavaScript's `undefined` is not a valid Convex value. Functions the return `undefined` or do not return will return `null` when called from a client. Use `null` instead.                             |
| Int64       | bigint      | `3n`                   | `v.int64()`                                    | Int64s only support BigInts between -2^63 and 2^63-1. Convex supports `bigint`s in most modern browsers.                                                                                              |
| Float64     | number      | `3.1`                  | `v.number()`                                   | Convex supports all IEEE-754 double-precision floating point numbers (such as NaNs). Inf and NaN are JSON serialized as strings.                                                                      |
| Boolean     | boolean     | `true`                 | `v.boolean()`                                  |
| String      | string      | `"abc"`                | `v.string()`                                   | Strings are stored as UTF-8 and must be valid Unicode sequences. Strings must be smaller than the 1MB total size limit when encoded as UTF-8.                                                         |
| Bytes       | ArrayBuffer | `new ArrayBuffer(8)`   | `v.bytes()`                                    | Convex supports first class bytestrings, passed in as `ArrayBuffer`s. Bytestrings must be smaller than the 1MB total size limit for Convex types.                                                     |
| Array       | Array]      | `[1, 3.2, "abc"]`      | `v.array(values)`                              | Arrays can have at most 8192 values.                                                                                                                                                                  |
| Object      | Object      | `{a: "abc"}`           | `v.object({property: value})`                  | Convex only supports "plain old JavaScript objects" (objects that do not have a custom prototype). Objects can have at most 1024 entries. Field names must be nonempty and not start with "$" or "_". |
| Record      | Record      | `{"a": "1", "b": "2"}` | `v.record(keys, values)`                       | Records are objects at runtime, but can have dynamic keys. Keys must be only ASCII characters, nonempty, and not start with "$" or "_".                                                               |

### Function registration
- Use `internalQuery`, `internalMutation`, and `internalAction` to register internal functions. These functions are private and aren't part of an app's API. They can only be called by other Convex functions. These functions are always imported from `./_generated/server`.
- Use `query`, `mutation`, and `action` to register public functions. These functions are part of the public API and are exposed to the public Internet. Do NOT use `query`, `mutation`, or `action` to register sensitive internal functions that should be kept private.
- You CANNOT register a function through the `api` or `internal` objects.
- ALWAYS include argument and return validators for all Convex functions. This includes all of `query`, `internalQuery`, `mutation`, `internalMutation`, `action`, and `internalAction`. If a function doesn't return anything, include `returns: v.null()` as its output validator.
- If the JavaScript implementation of a Convex function doesn't have a return value, it implicitly returns `null`.

### Function calling
- Use `ctx.runQuery` to call a query from a query, mutation, or action.
- Use `ctx.runMutation` to call a mutation from a mutation or action.
- Use `ctx.runAction` to call an action from an action.
- ONLY call an action from another action if you need to cross runtimes (e.g. from V8 to Node). Otherwise, pull out the shared code into a helper async function and call that directly instead.
- Try to use as few calls from actions to queries and mutations as possible. Queries and mutations are transactions, so splitting logic up into multiple calls introduces the risk of race conditions.
- All of these calls take in a `FunctionReference`. Do NOT try to pass the callee function directly into one of these calls.
- When using `ctx.runQuery`, `ctx.runMutation`, or `ctx.runAction` to call a function in the same file, specify a type annotation on the return value to work around TypeScript circularity limitations. For example,
```
export const f = query({
  args: { name: v.string() },
  returns: v.string(),
  handler: async (ctx, args) => {
    return "Hello " + args.name;
  },
});

export const g = query({
  args: {},
  returns: v.null(),
  handler: async (ctx, args) => {
    const result: string = await ctx.runQuery(api.example.f, { name: "Bob" });
    return null;
  },
});
```

### Function references
- Function references are pointers to registered Convex functions.
- Use the `api` object defined by the framework in `convex/_generated/api.ts` to call public functions registered with `query`, `mutation`, or `action`.
- Use the `internal` object defined by the framework in `convex/_generated/api.ts` to call internal (or private) functions registered with `internalQuery`, `internalMutation`, or `internalAction`.
- Convex uses file-based routing, so a public function defined in `convex/example.ts` named `f` has a function reference of `api.example.f`.
- A private function defined in `convex/example.ts` named `g` has a function reference of `internal.example.g`.
- Functions can also registered within directories nested within the `convex/` folder. For example, a public function `h` defined in `convex/messages/access.ts` has a function reference of `api.messages.access.h`.

### Api design
- Convex uses file-based routing, so thoughtfully organize files with public query, mutation, or action functions within the `convex/` directory.
- Use `query`, `mutation`, and `action` to define public functions.
- Use `internalQuery`, `internalMutation`, and `internalAction` to define private, internal functions.

### Pagination
- Paginated queries are queries that return a list of results in incremental pages.
- You can define pagination using the following syntax:

```ts
import { v } from "convex/values";
import { query, mutation } from "./_generated/server";
import { paginationOptsValidator } from "convex/server";
export const listWithExtraArg = query({
    args: { paginationOpts: paginationOptsValidator, author: v.string() },
    handler: async (ctx, args) => {
        return await ctx.db
        .query("messages")
        .filter((q) => q.eq(q.field("author"), args.author))
        .order("desc")
        .paginate(args.paginationOpts);
    },
});
```
Note: `paginationOpts` is an object with the following properties:
- `numItems`: the maximum number of documents to return (the validator is `v.number()`)
- `cursor`: the cursor to use to fetch the next page of documents (the validator is `v.union(v.string(), v.null())`)
- A query that ends in `.paginate()` returns an object that has the following properties:
                            - page (contains an array of documents that you fetches)
                            - isDone (a boolean that represents whether or not this is the last page of documents)
                            - continueCursor (a string that represents the cursor to use to fetch the next page of documents)


## Validator guidelines
- `v.bigint()` is deprecated for representing signed 64-bit integers. Use `v.int64()` instead.
- Use `v.record()` for defining a record type. `v.map()` and `v.set()` are not supported.

## Schema guidelines
- Always define your schema in `convex/schema.ts`.
- Always import the schema definition functions from `convex/server`:
- System fields are automatically added to all documents and are prefixed with an underscore. The two system fields that are automatically added to all documents are `_creationTime` which has the validator `v.number()` and `_id` which has the validator `v.id(tableName)`.
- Always include all index fields in the index name. For example, if an index is defined as `["field1", "field2"]`, the index name should be "by_field1_and_field2".
- Index fields must be queried in the same order they are defined. If you want to be able to query by "field1" then "field2" and by "field2" then "field1", you must create separate indexes.
## Typescript guidelines
- You can use the helper typescript type `Id` imported from './_generated/dataModel' to get the type of the id for a given table. For example if there is a table called 'users' you can use `Id<'users'>` to get the type of the id for that table.
- If you need to define a `Record