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Lesson 5.3: Defining constraints

Constraining attribute values

The values of string attribute types can be constrained with a regex statement, which specifies a Java regex pattern string that is validated against when instantiating the attribute type. In the following example, we require that the value of status instances must be one of "paid", "dispatched", "delivered", "returned", or "canceled".

define
status sub attribute,
    value string,
    regex "^(paid|dispatched|delivered|returned|canceled)$";
order owns status;

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Regex constraints apply directly to attributes, regardless of the owning type. In this example, if another entity or relation type owned status, it would also be restricted to the preset values.

The regex constraint is the only attribute value constraint in TypeDB 2.x. TypeDB 3.0 will feature other value constraints, such as ranges for numeric values and enums. To learn more about this and other powerful new features, see the TypeDB 3.0 roadmap.

Constraining attribute ownerships

TypeQL provides syntax for defining key and unique constraints on attribute ownerships via annotations. An annotation is an additional constraint applied to a statement, denoted by an @ prefix. The following example defines five such constraints.

define
id sub attribute, value string;
book owns isbn-13 @key,
    owns isbn-10 @unique;
user owns id @key;
order owns id @key;
review owns id @key;

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When applied to an ownership statement in a Define query, the @key and @unique annotations apply a key or unique constraint respectively to that ownership. This is different to regex statements, which apply to the attribute itself.

A key constraint requires that instances of the owner type own exactly one instance of the attribute type, and that it must be uniquely owned by the owner type. In the example above, every instance of book must own exactly one instance of isbn-13, and no two instances of book can own the same instance of isbn-13.

A unique constraint requires only that instances of the attribute type are uniquely owned by the owner type. In the example above, no two instances of book can own the same instance of isbn-10, but an instance of book can own any number of instances of isbn-10 (including none).

Ownership annotations apply to the specific ownerships they are defined on rather than to the attribute in general. In the example above, key constraints are applied to the ownership of id by user, order, and review. This means that, while two instances of user (or two of order, or two of review) could not own the same instance of id, it is perfectly permissible for an instance of user and an instance of order to own the same instance of id.