Filtering by relations

ant.Hasfunc Has[R any](rel *[]R, conds ...Cond) CondHas matches rows with at least one related row in a one-to-many relation that meets conds. filters rows by what they're related to, without loading anything. Each one becomes an EXISTS inside the same query, so it costs no extra round trip.

Has a related row

writers, err := db.Users.Where(ant.Has(&U.Posts)).All(ctx)

Add conditions on the related row.

drafting, err := db.Users.Where(ant.Has(&U.Posts, ant.Eq(&P.Published, false))).All(ctx)

Has none

silent, err := db.Users.Where(ant.HasNone(&U.Posts)).All(ctx)

HasNone with conditions matches rows with no related row that meets them.

The other direction

ant.HasOnefunc HasOne[R any](rel **R, conds ...Cond) CondHasOne matches rows with a related row in a many-to-one or one-to-one relation that meets conds. follows a many-to-one or one-to-one relation.

byAdults, err := db.Posts.Where(ant.HasOne(&P.User, ant.Gt(&U.Age, 18))).All(ctx)

Combining

These are conditions like any other.

young, err := db.Users.Where(ant.Has(&U.Posts), ant.Lt(&U.Age, 18)).All(ctx)

same, err := db.Users.Where(ant.Not(ant.Has(&U.Posts))).Count(ctx)

They work on many-to-many and through relations too, and a global filter on the related model still applies.

Build it at run time

ant.Has needs the related model's configuration, which exists once a context has opened. Call it where the query is built, not in a package variable.

See it tested: tests/features/relations/has_test.go