Check Constraints

[evantrimboli]

Is your feature request related to a problem? Please describe.
To keep data layer logic centralized, it would be nice to be able to specify check constraints on fields.

Describe the solution you'd like

@Entity()
class Product {
  @Property({
    check: (productMeta) => `${productMeta.price.dbName} >= 0`,
  })
  price!: number
}

The sql generated should be something like:

CREATE TABLE products (
    price numeric CHECK (price >= 0)
);

The productMeta would be some sort of construct to access the underlying column names to be able to construct the constraint according to the naming strategy. There are a few ways this could go down, not sure what would be most idiomatic.

Describe alternatives you've considered

• They could be manually added to migrations
• Handle these at the API layer

Additional context
N/A

[DASPRiD]

Check constraints can also be added to a table directly. This is actually how TypeORM did implement them. The resulting SQL from that usually looks something like this:

CREATE TABLE foo (
  price numeric NOT NULL,
  CONSTRAINT foo_bar CHECK (price >= 0)
)

This should be fairly easy to implement as a @Check annotation to the @Entity. We could basically allow the developer to write any SQL check expression, and then diff on the expression for migrations. This would also be the most flexible approach. For instance:

@Entity()
@Check('price >= 0')
class Foo {
  @Property()
  price : number;
}