Why do SurrealDB updates fail after I add a field with a TYPE?

DEFINE FIELD with a required type on an existing table

Critical: SurrealDB refuses the migration, loses data, or leaks a credential.

What happens

Observed on SurrealDB 3.0.2: CREATE customer:1, then DEFINE FIELD region ON customer TYPE string succeeds, and the next UPDATE customer:1 SET name = 'b' fails with "Couldn't coerce value for field `region` of `customer:1`: Expected `string` but found `NONE`". The same happens with DEFAULT 'eu'; DEFAULT ALWAYS, VALUE, option<string> and string | none all let the update through.

Why it is dangerous on a populated table

SurrealDB checks a schema change against new writes, not the records already stored, so an empty table hides it: on a populated one every old record is a write waiting to fail, and whole-table work runs for the length of the table in one transaction.

Fires on

DEFINE FIELD region ON TABLE customer TYPE string;

The safe pattern

DEFINE FIELD region ON TABLE customer TYPE string DEFAULT ALWAYS 'eu';

Fixtures

The rule ships with these files and the test suite runs them on every change: the first set must fire, the second must stay silent.

DEFINE FIELD IF NOT EXISTS loyalty_points ON customer TYPE int;

-- DEFAULT only fills the field on CREATE; existing records still lack it.
DEFINE FIELD region ON TABLE customer TYPE string DEFAULT 'eu';

DEFINE FIELD region ON TABLE customer TYPE string;

DEFINE FIELD region ON TABLE customer TYPE string;
UPDATE customer SET region = 'eu' WHERE region IS NONE;

DEFINE FIELD updated_at ON TABLE customer TYPE datetime VALUE time::now();

DEFINE FIELD region ON TABLE customer TYPE string DEFAULT ALWAYS 'eu';

DEFINE FIELD address.city ON TABLE customer TYPE string;

DEFINE TABLE customer SCHEMAFULL;
DEFINE FIELD region ON TABLE customer TYPE string;

DEFINE FIELD region ON TABLE customer TYPE option<string>;

DEFINE FIELD region ON TABLE customer TYPE string | none;

How to check locally

npx bolvrk check migration.surql --engine=surrealdb