Constraints​

This section assumes a basic understanding of EdgeQL.

Constraints gives users fine-grained control over which data is considered valid. The can be defined on properties, links, object types, and custom scalars.

Built-in constraints​

For convenience, EdgeDB provides some pre-defined constraints. Click the name of a given constraint for the full documentation.

The expression constraint is used to define custom constraint logic. Inside custom constraints, the keyword __subject__ can used to reference the value being constrained.

Constraints on properties​

The constraint below uses the built-in len() function, which returns the length of a string.

type User {
  required property username -> str {
    # as custom constraint
    constraint expression on (len(__subject__) < 25);
    # with built-in
    constraint min_len_value(25);
  };
}

Constraints on object types​

Constraints can be defined on object types. This is useful when the constraint logic must reference multiple links or properties.

Inside an object type declaration, you can omit __subject__ and simple refer to properties with the leading dot notation (e.g. .<name>).

type ConstrainedVector {
  required property x -> float64;
  required property y -> float64;
  constraint expression on (
    .x ^ 2 + .y ^ 2 <= 25
  );
}

Constraints on links​

When defining a constraint on a link, __subject__ refers to the link itself. This is commonly used add constraints to link properties.

type User {
  property name -> str;
  multi link friends -> User {
    single property strength -> float64;
    constraint expression on (
      __subject__@strength >= 0
    );
  }
}

Constraints on custom scalars​

Custom scalar types can be constrained.

scalar type username extending str {
  constraint regexp(r'^[A-Za-z0-9_]{4,20}$');
}

Note: you can’t use exclusive constraints on custom scalar types, as the concept of exclusivity is only defined in the context of a given object type.

Use expression constraints to declare custom constraints using arbitrary EdgeQL expressions. The example below uses the built-in str_trim() function.

scalar type title extending str {
  constraint expression on (
    __subject__ = str_trim(__subject__)
  );
}

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