convex-helpers-guide

What this skill does

# 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 member = await ctx.db
      .query("organizationMembers")
      .withIndex("by_org_and_user", q =>
        q.eq("orgId", args.orgId).eq("userId", user._id)
      )
      .unique();

    if (!member) {
      throw new Error("Not authorized for this organization");
    }

    // Inject org context
    return {
      ctx: {
        ...ctx,
        user,
        orgId: args.orgId,
        role: member.role
      },
      args
    };
  },
});

// Usage - data automatically scoped to organization
export const getOrgProjects = orgQuery({
  args: { orgId: v.id("organizations") },
  handler: async (ctx) => {
    // ctx.user and ctx.orgId automatically available and verified!
    return await ctx.db
      .query("projects")
      .withIndex("by_org", q => q.eq("orgId", ctx.orgId))
      .collect();
  },
});
```

**Example: Role-Based Access Control**
```typescript
import { customMutation } from "convex-helpers/server/customFunctions";
import { mutation } from "../_generated/server";

export const adminMutation = customMutation(mutation, {
  args: {},
  input: async (ctx, args) => {
    const user = await getCurrentUser(ctx);

    if (user.role !== "admin") {
      throw new Error("Admin access required");
    }

    return { ctx: { ...ctx, user }, args };
  },
});

// Usage - only admins can call this
export const deleteUser = adminMutation({
  args: { userId: v.id("users") },
  handler: async (ctx, args) => {
    // Only admins reach this code
    await ctx.db.delete(args.userId);
  },
});
```

### 3. Filter Helper

Apply complex TypeScript filters to database queries.

**Use when:**
- Need to filter by computed values
- Filtering logic is too complex for indexes
- Working with small result sets

**Example:**
```typescript
import { filter } from "convex-helpers/server/filter";

export const getActiveTasks = query({
  handler: async (ctx) => {
    const now = Date.now();
    const threeDaysAgo = now - 3 * 24 * 60 * 60 * 1000;

    return await filter(
      ctx.db.query("tasks"),
      (task) =>
        !task.completed &&
        task.createdAt > threeDaysAgo &&
        task.priority === "high"
    ).collect();
  },
});
```

**Note:** Still prefer indexes when possible! Use filter for complex logic that can't be indexed.

### 4. Sessions

Track users across requests even when not logged in.

**Use when:**
- Need to track anonymous users
- Building shopping cart for guests
- Tracking user behavior before signup
- A/B testing without auth

**Setup:**
```typescript
// convex/sessions.ts
import { SessionIdArg } from "convex-helpers/server/sessions";
import { query } from "./_generated/server";

export const trackView = query({
  args: {
    ...SessionIdArg, // Adds sessionId: v.string()
    pageUrl: v.string(),
  },
  handler: async (ctx, args) => {
    await ctx.db.insert("pageViews", {
      sessionId: args.sessionId,
      pageUrl: args.pageUrl,
      timestamp: Date.now(),
    });
  },
});
```

**Client (React):**
```typescript
import { useSessionId } from "convex-helpers/react/sessions";
import { useQuery } from "convex/react";
import { api } from "../convex/_generated/api";

function MyComponent() {
  const sessionId = useSessionId();

  // Automatically includes sessionId in all requests
  useQuery(api.sessions.trackView, {
    sessionId,
    pageUrl: window.location.href,
  });
}
```

### 5. Zod Validation

Use Zod schemas instead of Convex validators.

**Use when:**
- Already using Zod in your project
- Want more complex validation logic
- Need custom error messages

**Example:**
```typescript
import { zCustomQuery } from "convex-helpers/server/zod";
import { z } from "zod";
import { query } from "./_generated/server";

const argsSchema = z.object({
  email: z.string().email(),
  age: z.number().min(18).max(120),
});

export const createUser = zCustomQuery(query, {
  args: argsSchema,
  handler: async (ctx, args) => {
    // args is typed from Zod schema
    return await ctx.db.insert("users", args);
  },
});
```

### 6. Alternative: Row-Level Security Helper

**Note:** Convex recommends using **custom functions** (see #2 above) as the primary data protection pattern. This RLS helper is an alternative approach that mimics t