valv

Writes

valv can let an agent change data, not just read it. Writes are off until you both allow them in a policy and expose the tool, and they carry stronger guarantees than reads. This page covers the write grammar, the policy axes, and the rules valv enforces.

Writes are off by default

There are three write tools: create, update, and delete. Each is its own tool and its own policy axis, and all three default to denied. You turn a write on in two places: allow it in the policy, and expose its tool. See Tools & providers for exposing the tools.

valv.policy("orders", (ctx) => ({
  read: { tenant_id: ctx.tenant.id },
  create: { tenant_id: ctx.tenant.id }, // tenant_id is force-set on insert
  update: { tenant_id: ctx.tenant.id }, // AND-injected into the WHERE
  delete: false, // never deletable
  fields: { readOnly: ["status"] }, // readable, not writable
}))

What the guarantees are

The write rules close the gaps a raw INSERT or UPDATE would leave open:

  • create force-injects the policy’s owned fields, such as tenant_id, onto the row. The model can’t choose, omit, or override them, so it can’t aim a new row at another tenant.
  • update and delete AND the policy predicate into your where, and the where is required. There’s no implicit “all rows,” and the model can only touch rows already in its scope.
  • Writable is separate from readable. The columns a write sets are checked against a writable allowlist. Scope columns, sensitive fields, and readOnly fields are readable but not writable.
  • A where on a write can only filter by columns the caller is allowed to read.

Calling writes from your code

Each write has a method on the valv instance. Like reads, they run through the full validate-and-inject pipeline:

await valv.create({ from: "orders", values: { status: "pending", total: 1200 } }, ctx)

await valv.update(
  { from: "orders", set: { status: "shipped" }, where: { /* Expr */ } },
  ctx,
)

Database support

Writes work on all Prisma databases (Postgres, MySQL, SQLite, and CockroachDB). ClickHouse supports create (insert) only.

Next steps