Electric — Schema and Shapes

// Each shape syncs one table — join client-side
const todoStream = new ShapeStream({ url: '/api/todos' })
const userStream = new ShapeStream({ url: '/api/users' })

// With TanStack DB, use .join() in live queries:
// q.from({ todo: todoCollection })
//   .join({ user: userCollection }, ({ todo, user }) => eq(todo.userId, user.id))

Choose replica mode

// Default: only changed columns sent on update
const stream = new ShapeStream({ url: '/api/todos' })

// Full: all columns + old_value on updates (more bandwidth, needed for diffs)
const stream = new ShapeStream({
  url: '/api/todos',
  params: { replica: 'full' },
})

Backend txid handshake for optimistic writes

Call pg_current_xact_id()::xid::text inside the same transaction as your mutation. If you query it outside the transaction, you get a different txid and the client will never reconcile.

// API endpoint — txid MUST be in the same transaction as the INSERT
app.post('/api/todos', async (req, res) => {
  const client = await pool.connect()
  try {
    await client.query('BEGIN')
    const result = await client.query(
      'INSERT INTO todos (id, text, org_id) VALUES ($1, $2, $3) RETURNING id',
      [crypto.randomUUID(), req.body.text, req.body.orgId]
    )
    const txResult = await client.query(
      'SELECT pg_current_xact_id()::xid::text AS txid'
    )
    await client.query('COMMIT')
    // txid accepts number | bigint | `${bigint}`
    res.json({ id: result.rows[0].id, txid: parseInt(txResult.rows[0].txid) })
  } finally {
    client.release()
  }
})

// Client awaits txid before dropping optimistic state
await todoCollection.utils.awaitTxId(txid)

Common Mistakes

HIGH Designing shapes that span multiple tables

Wrong:

const stream = new ShapeStream({
  url: '/api/data',
  params: {
    table: 'todos JOIN users ON todos.user_id = users.id',
  },
})

Correct:

const todoStream = new ShapeStream({ url: '/api/todos' })
const userStream = new ShapeStream({ url: '/api/users' })

Shapes are single-table only. Cross-table data requires multiple shapes joined client-side via TanStack DB live queries.

Source: AGENTS.md:104-105

MEDIUM Using enum columns without casting to text in WHERE

Wrong:

// Proxy route
originUrl.searchParams.set('where', "status IN ('active', 'done')")

Correct:

originUrl.searchParams.set('where', "status::text IN ('active', 'done')")

Enum types in WHERE clauses require explicit ::text cast. Without it, the query may fail or return unexpected results.

Source: packages/sync-service/lib/electric/replication/eval/env/known_functions.ex

HIGH Not setting up txid handshake for optimistic writes

Wrong:

// Backend: just INSERT, return id
app.post('/api/todos', async (req, res) => {
  const result = await db.query(
    'INSERT INTO todos (text) VALUES ($1) RETURNING id',
    [req.body.text]
  )
  res.json({ id: result.rows[0].id })
})

Correct:

// Backend: INSERT and return txid in same transaction
app.post('/api/todos', async (req, res) => {
  const client = await pool.connect()
  try {
    await client.query('BEGIN')
    const result = await client.query(
      'INSERT INTO todos (text) VALUES ($1) RETURNING id',
      [req.body.text]
    )
    const txResult = await client.query(
      'SELECT pg_current_xact_id()::xid::text AS txid'
    )
    await client.query('COMMIT')
    res.json({ id: result.rows[0].id, txid: parseInt(txResult.rows[0].txid) })
  } finally {
    client.release()
  }
})

Without txid, the UI flickers when optimistic state is dropped before the synced version arrives from Electric. The client uses awaitTxId(txid) to hold optimistic state until the real data syncs.

Source: AGENTS.md:116-119

See also: electric-shapes/SKILL.md — Shapes are immutable; dynamic filters require new ShapeStream instances. See also: electric-orm/SKILL.md — Schema design affects both shapes (read) and ORM queries (write).

Version

Targets @electric-sql/client v1.5.10.