convex-migrations

Evolve your Convex database schema safely with patterns for adding fields, backfilling data, removing deprecated fields, and maintaining zero-downtime deployments.

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Install skill "convex-migrations" with this command: npx skills add jstarfilms/vibecode-protocol-suite/jstarfilms-vibecode-protocol-suite-convex-migrations

Convex Migrations

Evolve your Convex database schema safely with patterns for adding fields, backfilling data, removing deprecated fields, and maintaining zero-downtime deployments.

Documentation Sources

Before implementing, do not assume; fetch the latest documentation:

Instructions

Migration Philosophy

Convex handles schema evolution differently than traditional databases:

  • No explicit migration files or commands

  • Schema changes deploy instantly with npx convex dev

  • Existing data is not automatically transformed

  • Use optional fields and backfill mutations for safe migrations

Adding New Fields

Start with optional fields, then backfill:

// Step 1: Add optional field to schema // convex/schema.ts import { defineSchema, defineTable } from "convex/server"; import { v } from "convex/values";

export default defineSchema({ users: defineTable({ name: v.string(), email: v.string(), // New field - start as optional avatarUrl: v.optional(v.string()), }), });

// Step 2: Update code to handle both cases // convex/users.ts import { query } from "./_generated/server"; import { v } from "convex/values";

export const getUser = query({ args: { userId: v.id("users") }, returns: v.union( v.object({ _id: v.id("users"), name: v.string(), email: v.string(), avatarUrl: v.union(v.string(), v.null()), }), v.null() ), handler: async (ctx, args) => { const user = await ctx.db.get(args.userId); if (!user) return null;

return {
  _id: user._id,
  name: user.name,
  email: user.email,
  // Handle missing field gracefully
  avatarUrl: user.avatarUrl ?? null,
};

}, });

// Step 3: Backfill existing documents // convex/migrations.ts import { internalMutation } from "./_generated/server"; import { internal } from "./_generated/api"; import { v } from "convex/values";

const BATCH_SIZE = 100;

export const backfillAvatarUrl = internalMutation({ args: { cursor: v.optional(v.string()), }, returns: v.object({ processed: v.number(), hasMore: v.boolean(), }), handler: async (ctx, args) => { const result = await ctx.db .query("users") .paginate({ numItems: BATCH_SIZE, cursor: args.cursor ?? null });

let processed = 0;
for (const user of result.page) {
  // Only update if field is missing
  if (user.avatarUrl === undefined) {
    await ctx.db.patch(user._id, {
      avatarUrl: generateDefaultAvatar(user.name),
    });
    processed++;
  }
}

// Schedule next batch if needed
if (!result.isDone) {
  await ctx.scheduler.runAfter(0, internal.migrations.backfillAvatarUrl, {
    cursor: result.continueCursor,
  });
}

return {
  processed,
  hasMore: !result.isDone,
};

}, });

function generateDefaultAvatar(name: string): string { return https://api.dicebear.com/7.x/initials/svg?seed=${encodeURIComponent(name)}; }

// Step 4: After backfill completes, make field required // convex/schema.ts export default defineSchema({ users: defineTable({ name: v.string(), email: v.string(), avatarUrl: v.string(), // Now required }), });

Removing Fields

Remove field usage before removing from schema:

// Step 1: Stop using the field in queries and mutations // Mark as deprecated in code comments

// Step 2: Remove field from schema (make optional first if needed) // convex/schema.ts export default defineSchema({ posts: defineTable({ title: v.string(), content: v.string(), authorId: v.id("users"), // legacyField: v.optional(v.string()), // Remove this line }), });

// Step 3: Optionally clean up existing data // convex/migrations.ts export const removeDeprecatedField = internalMutation({ args: { cursor: v.optional(v.string()), }, returns: v.null(), handler: async (ctx, args) => { const result = await ctx.db .query("posts") .paginate({ numItems: 100, cursor: args.cursor ?? null });

for (const post of result.page) {
  // Use replace to remove the field entirely
  const { legacyField, ...rest } = post as typeof post & { legacyField?: string };
  if (legacyField !== undefined) {
    await ctx.db.replace(post._id, rest);
  }
}

if (!result.isDone) {
  await ctx.scheduler.runAfter(0, internal.migrations.removeDeprecatedField, {
    cursor: result.continueCursor,
  });
}

return null;

}, });

Renaming Fields

Renaming requires copying data to new field, then removing old:

// Step 1: Add new field as optional // convex/schema.ts export default defineSchema({ users: defineTable({ userName: v.string(), // Old field displayName: v.optional(v.string()), // New field }), });

// Step 2: Update code to read from new field with fallback export const getUser = query({ args: { userId: v.id("users") }, returns: v.object({ _id: v.id("users"), displayName: v.string(), }), handler: async (ctx, args) => { const user = await ctx.db.get(args.userId); if (!user) throw new Error("User not found");

return {
  _id: user._id,
  // Read new field, fall back to old
  displayName: user.displayName ?? user.userName,
};

}, });

// Step 3: Backfill to copy data export const backfillDisplayName = internalMutation({ args: { cursor: v.optional(v.string()) }, returns: v.null(), handler: async (ctx, args) => { const result = await ctx.db .query("users") .paginate({ numItems: 100, cursor: args.cursor ?? null });

for (const user of result.page) {
  if (user.displayName === undefined) {
    await ctx.db.patch(user._id, {
      displayName: user.userName,
    });
  }
}

if (!result.isDone) {
  await ctx.scheduler.runAfter(0, internal.migrations.backfillDisplayName, {
    cursor: result.continueCursor,
  });
}

return null;

}, });

// Step 4: After backfill, update schema to make new field required // and remove old field export default defineSchema({ users: defineTable({ // userName removed displayName: v.string(), }), });

Adding Indexes

Add indexes before using them in queries:

// Step 1: Add index to schema // convex/schema.ts export default defineSchema({ posts: defineTable({ title: v.string(), authorId: v.id("users"), publishedAt: v.optional(v.number()), status: v.string(), }) .index("by_author", ["authorId"]) // New index .index("by_status_and_published", ["status", "publishedAt"]), });

// Step 2: Deploy schema change // Run: npx convex dev

// Step 3: Now use the index in queries export const getPublishedPosts = query({ args: {}, returns: v.array(v.object({ _id: v.id("posts"), title: v.string(), publishedAt: v.number(), })), handler: async (ctx) => { const posts = await ctx.db .query("posts") .withIndex("by_status_and_published", (q) => q.eq("status", "published") ) .order("desc") .take(10);

return posts
  .filter((p) => p.publishedAt !== undefined)
  .map((p) => ({
    _id: p._id,
    title: p.title,
    publishedAt: p.publishedAt!,
  }));

}, });

Changing Field Types

Type changes require careful migration:

// Example: Change from string to number for a "priority" field

// Step 1: Add new field with new type // convex/schema.ts export default defineSchema({ tasks: defineTable({ title: v.string(), priority: v.string(), // Old: "low", "medium", "high" priorityLevel: v.optional(v.number()), // New: 1, 2, 3 }), });

// Step 2: Backfill with type conversion export const migratePriorityToNumber = internalMutation({ args: { cursor: v.optional(v.string()) }, returns: v.null(), handler: async (ctx, args) => { const result = await ctx.db .query("tasks") .paginate({ numItems: 100, cursor: args.cursor ?? null });

const priorityMap: Record<string, number> = {
  low: 1,
  medium: 2,
  high: 3,
};

for (const task of result.page) {
  if (task.priorityLevel === undefined) {
    await ctx.db.patch(task._id, {
      priorityLevel: priorityMap[task.priority] ?? 1,
    });
  }
}

if (!result.isDone) {
  await ctx.scheduler.runAfter(0, internal.migrations.migratePriorityToNumber, {
    cursor: result.continueCursor,
  });
}

return null;

}, });

// Step 3: Update code to use new field export const getTask = query({ args: { taskId: v.id("tasks") }, returns: v.object({ _id: v.id("tasks"), title: v.string(), priorityLevel: v.number(), }), handler: async (ctx, args) => { const task = await ctx.db.get(args.taskId); if (!task) throw new Error("Task not found");

const priorityMap: Record<string, number> = {
  low: 1,
  medium: 2,
  high: 3,
};

return {
  _id: task._id,
  title: task.title,
  priorityLevel: task.priorityLevel ?? priorityMap[task.priority] ?? 1,
};

}, });

// Step 4: After backfill, update schema export default defineSchema({ tasks: defineTable({ title: v.string(), // priority field removed priorityLevel: v.number(), }), });

Migration Runner Pattern

Create a reusable migration system:

// convex/schema.ts import { defineSchema, defineTable } from "convex/server"; import { v } from "convex/values";

export default defineSchema({ migrations: defineTable({ name: v.string(), startedAt: v.number(), completedAt: v.optional(v.number()), status: v.union( v.literal("running"), v.literal("completed"), v.literal("failed") ), error: v.optional(v.string()), processed: v.number(), }).index("by_name", ["name"]),

// Your other tables... });

// convex/migrations.ts import { internalMutation, internalQuery } from "./_generated/server"; import { internal } from "./_generated/api"; import { v } from "convex/values";

// Check if migration has run export const hasMigrationRun = internalQuery({ args: { name: v.string() }, returns: v.boolean(), handler: async (ctx, args) => { const migration = await ctx.db .query("migrations") .withIndex("by_name", (q) => q.eq("name", args.name)) .first(); return migration?.status === "completed"; }, });

// Start a migration export const startMigration = internalMutation({ args: { name: v.string() }, returns: v.id("migrations"), handler: async (ctx, args) => { // Check if already exists const existing = await ctx.db .query("migrations") .withIndex("by_name", (q) => q.eq("name", args.name)) .first();

if (existing) {
  if (existing.status === "completed") {
    throw new Error(`Migration ${args.name} already completed`);
  }
  if (existing.status === "running") {
    throw new Error(`Migration ${args.name} already running`);
  }
  // Reset failed migration
  await ctx.db.patch(existing._id, {
    status: "running",
    startedAt: Date.now(),
    error: undefined,
    processed: 0,
  });
  return existing._id;
}

return await ctx.db.insert("migrations", {
  name: args.name,
  startedAt: Date.now(),
  status: "running",
  processed: 0,
});

}, });

// Update migration progress export const updateMigrationProgress = internalMutation({ args: { migrationId: v.id("migrations"), processed: v.number(), }, returns: v.null(), handler: async (ctx, args) => { const migration = await ctx.db.get(args.migrationId); if (!migration) return null;

await ctx.db.patch(args.migrationId, {
  processed: migration.processed + args.processed,
});

return null;

}, });

// Complete a migration export const completeMigration = internalMutation({ args: { migrationId: v.id("migrations") }, returns: v.null(), handler: async (ctx, args) => { await ctx.db.patch(args.migrationId, { status: "completed", completedAt: Date.now(), }); return null; }, });

// Fail a migration export const failMigration = internalMutation({ args: { migrationId: v.id("migrations"), error: v.string(), }, returns: v.null(), handler: async (ctx, args) => { await ctx.db.patch(args.migrationId, { status: "failed", error: args.error, }); return null; }, });

// convex/migrations/addUserTimestamps.ts import { internalMutation } from "../_generated/server"; import { internal } from "../_generated/api"; import { v } from "convex/values";

const MIGRATION_NAME = "add_user_timestamps_v1"; const BATCH_SIZE = 100;

export const run = internalMutation({ args: { migrationId: v.optional(v.id("migrations")), cursor: v.optional(v.string()), }, returns: v.null(), handler: async (ctx, args) => { // Initialize migration on first run let migrationId = args.migrationId; if (!migrationId) { const hasRun = await ctx.runQuery(internal.migrations.hasMigrationRun, { name: MIGRATION_NAME, }); if (hasRun) { console.log(Migration ${MIGRATION_NAME} already completed); return null; } migrationId = await ctx.runMutation(internal.migrations.startMigration, { name: MIGRATION_NAME, }); }

try {
  const result = await ctx.db
    .query("users")
    .paginate({ numItems: BATCH_SIZE, cursor: args.cursor ?? null });

  let processed = 0;
  for (const user of result.page) {
    if (user.createdAt === undefined) {
      await ctx.db.patch(user._id, {
        createdAt: user._creationTime,
        updatedAt: user._creationTime,
      });
      processed++;
    }
  }

  // Update progress
  await ctx.runMutation(internal.migrations.updateMigrationProgress, {
    migrationId,
    processed,
  });

  // Continue or complete
  if (!result.isDone) {
    await ctx.scheduler.runAfter(0, internal.migrations.addUserTimestamps.run, {
      migrationId,
      cursor: result.continueCursor,
    });
  } else {
    await ctx.runMutation(internal.migrations.completeMigration, {
      migrationId,
    });
    console.log(`Migration ${MIGRATION_NAME} completed`);
  }
} catch (error) {
  await ctx.runMutation(internal.migrations.failMigration, {
    migrationId,
    error: String(error),
  });
  throw error;
}

return null;

}, });

Examples

Schema with Migration Support

// convex/schema.ts import { defineSchema, defineTable } from "convex/server"; import { v } from "convex/values";

export default defineSchema({ // Migration tracking migrations: defineTable({ name: v.string(), startedAt: v.number(), completedAt: v.optional(v.number()), status: v.union( v.literal("running"), v.literal("completed"), v.literal("failed") ), error: v.optional(v.string()), processed: v.number(), }).index("by_name", ["name"]),

// Users table with evolved schema users: defineTable({ // Original fields name: v.string(), email: v.string(),

// Added in migration v1
createdAt: v.optional(v.number()),
updatedAt: v.optional(v.number()),

// Added in migration v2
avatarUrl: v.optional(v.string()),

// Added in migration v3
settings: v.optional(v.object({
  theme: v.string(),
  notifications: v.boolean(),
})),

}) .index("by_email", ["email"]) .index("by_createdAt", ["createdAt"]),

// Posts table with indexes for common queries posts: defineTable({ title: v.string(), content: v.string(), authorId: v.id("users"), status: v.union( v.literal("draft"), v.literal("published"), v.literal("archived") ), publishedAt: v.optional(v.number()), createdAt: v.number(), updatedAt: v.number(), }) .index("by_author", ["authorId"]) .index("by_status", ["status"]) .index("by_author_and_status", ["authorId", "status"]) .index("by_publishedAt", ["publishedAt"]), });

Best Practices

  • Never run npx convex deploy unless explicitly instructed

  • Never run any git commands unless explicitly instructed

  • Always start with optional fields when adding new data

  • Backfill data in batches to avoid timeouts

  • Test migrations on development before production

  • Keep track of completed migrations to avoid re-running

  • Update code to handle both old and new data during transition

  • Remove deprecated fields only after all code stops using them

  • Use pagination for large datasets

  • Add appropriate indexes before running queries on new fields

Common Pitfalls

  • Making new fields required immediately - Breaks existing documents

  • Not handling undefined values - Causes runtime errors

  • Large batch sizes - Causes function timeouts

  • Forgetting to update indexes - Queries fail or perform poorly

  • Running migrations without tracking - May run multiple times

  • Removing fields before code update - Breaks existing functionality

  • Not testing on development - Production data issues

References

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