Schema migration strategies for evolving applications including adding new fields, backfilling data, removing deprecated fields, index migrations, and zero-downtime migration patterns
npxskills add flinstech/flins--skill "Convex Migrations"Loading…
Evolve your Convex database schema safely with patterns for adding fields, backfilling data, removing deprecated fields, and maintaining zero-downtime deployments.
Before implementing, do not assume; fetch the latest documentation:
Convex handles schema evolution differently than traditional databases:
npx convex devStart 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
}),
});
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 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(),
}),
});
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!,
}));
},
});
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(),
}),
});
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;
},
});
// 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"]),
});
npx convex deploy unless explicitly instructed
Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Set up and use 1Password CLI (op). Use when installing the CLI, enabling desktop app integration, signing in (single or multi-account), or reading/injecting/running secrets via op.
CLI to manage emails via IMAP/SMTP. Use `himalaya` to list, read, write, reply, forward, search, and organize emails from the terminal. Supports multiple accounts and message composition with MML (MIME Meta Language).
Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Set up and use 1Password CLI (op). Use when installing the CLI, enabling desktop app integration, signing in (single or multi-account), or reading/injecting/running secrets via op.
CLI to manage emails via IMAP/SMTP. Use `himalaya` to list, read, write, reply, forward, search, and organize emails from the terminal. Supports multiple accounts and message composition with MML (MIME Meta Language).