Convex Helpers Guide

# Convex Helpers Guide

Use convex-helpers to add common patterns and utilities to your Convex backend without reinventing the wheel.

## What is convex-helpers?

`convex-helpers` is the official collection of utilities that complement Convex. It provides battle-tested patterns for common backend needs.

**Installation:**
```bash
npm install convex-helpers
```

## Available Helpers

### 1. Relationship Helpers

Traverse relationships between tables in a readable, type-safe way.

**Use when:**
- Loading related data across tables
- Following foreign key relationships
- Building nested data structures

**Example:**
```typescript
import { getOneFrom, getManyFrom } from "convex-helpers/server/relationships";

export const getTaskWithUser = query({
  args: { taskId: v.id("tasks") },
  handler: async (ctx, args) => {
    const task = await ctx.db.get(args.taskId);
    if (!task) return null;

    // Get related user
    const user = await getOneFrom(
      ctx.db,
      "users",
      "by_id",
      task.userId,
      "_id"
    );

    // Get related comments
    const comments = await getManyFrom(
      ctx.db,
      "comments",
      "by_task",
      task._id,
      "taskId"
    );

    return { ...task, user, comments };
  },
});
```

**Key Functions:**
- `getOneFrom` - Get single related document
- `getManyFrom` - Get multiple related documents
- `getManyVia` - Get many-to-many relationships through junction table

### 2. Custom Functions (Data Protection) - MOST IMPORTANT

**This is Convex's alternative to Row Level Security (RLS).** Instead of database-level policies, use custom function wrappers to automatically add auth and access control to all queries and mutations.

Create wrapped versions of query/mutation/action with custom behavior.

**Use when:**
- **Data protection and access control** (PRIMARY USE CASE)
- Want to add auth logic to all functions
- Multi-tenant applications
- Role-based access control (RBAC)
- Need to inject common data into ctx
- Building internal-only functions
- Adding logging/monitoring to all functions

**Why this instead of RLS:**
- TypeScript, not SQL policies
- Full type safety
- Easy to test and debug
- More flexible than database policies
- Works across your entire backend

**Example: Custom Query with Auto-Auth**
```typescript
// convex/lib/customFunctions.ts
import { customQuery } from "convex-helpers/server/customFunctions";
import { query } from "../_generated/server";

export const authenticatedQuery = customQuery(
  query,
  {
    args: {}, // No additional args required
    input: async (ctx, args) => {
      const identity = await ctx.auth.getUserIdentity();
      if (!identity) {
        throw new Error("Not authenticated");
      }

      const user = await ctx.db
        .query("users")
        .withIndex("by_token", q =>
          q.eq("tokenIdentifier", identity.tokenIdentifier)
        )
        .unique();

      if (!user) throw new Error("User not found");

      // Add user to context
      return { ctx: { ...ctx, user }, args };
    },
  }
);

// Usage in your functions
export const getMyTasks = authenticatedQuery({
  handler: async (ctx) => {
    // ctx.user is automatically available!
    return await ctx.db
      .query("tasks")
      .withIndex("by_user", q => q.eq("userId", ctx.user._id))
      .collect();
  },
});
```

**Example: Multi-Tenant Data Protection**
```typescript
import { customQuery } from "convex-helpers/server/customFunctions";
import { query } from "../_generated/server";

// Organization-scoped query - automatic access control
export const orgQuery = customQuery(query, {
  args: { orgId: v.id("organizations") },
  input: async (ctx, args) => {
    const user = await getCurrentUser(ctx);

    // Verify user is a member of this organization
    const mem