Function OrderByNeighborsCount

dialect/sql/sqlgraph/graph.go:380–436

OrderByNeighborsCount appends ordering based on the number of neighbors. For example, order users by their number of posts.

(q *sql.Selector, s *Step, opts ...sql.OrderTermOption)

// OrderByNeighborsCount appends ordering based on the number of neighbors.
// For example, order users by their number of posts.
func OrderByNeighborsCount(q *sql.Selector, s *Step, opts ...sql.OrderTermOption) {
	var (
		join  *sql.Selector
		opt   = sql.NewOrderTermOptions(opts...)
		build = sql.Dialect(q.Dialect())
	)
	switch {
	case s.FromEdgeOwner():
		// For M2O and O2O inverse, the FK resides in the same table.
		// Hence, the order by is on the nullability of the column.
		x := func(b *sql.Builder) {
			b.Ident(s.From.Column)
			if opt.Desc {
				b.WriteOp(sql.OpNotNull)
			} else {
				b.WriteOp(sql.OpIsNull)
			}
		}
		q.OrderExpr(build.Expr(x))
	case s.ThroughEdgeTable():
		countAs := countAlias(q, s, opt)
		terms := []sql.OrderTerm{
			sql.OrderByCount("*", append([]sql.OrderTermOption{sql.OrderAs(countAs)}, opts...)...),
		}
		pk1 := s.Edge.Columns[0]
		if s.Edge.Inverse {
			pk1 = s.Edge.Columns[1]
		}
		joinT := build.Table(s.Edge.Table).Schema(s.Edge.Schema)
		join = build.Select(
			joinT.C(pk1),
		).From(joinT).GroupBy(joinT.C(pk1))
		selectTerms(join, terms)
		q.LeftJoin(join).
			On(
				q.C(s.From.Column),
				join.C(pk1),
			)
		orderTerms(q, join, terms)
	case s.ToEdgeOwner():
		countAs := countAlias(q, s, opt)
		terms := []sql.OrderTerm{
			sql.OrderByCount("*", append([]sql.OrderTermOption{sql.OrderAs(countAs)}, opts...)...),
		}
		edgeT := build.Table(s.Edge.Table).Schema(s.Edge.Schema)
		join = build.Select(
			edgeT.C(s.Edge.Columns[0]),
		).From(edgeT).GroupBy(edgeT.C(s.Edge.Columns[0]))
		selectTerms(join, terms)
		q.LeftJoin(join).
			On(
				q.C(s.From.Column),
				join.C(s.Edge.Columns[0]),
			)
		orderTerms(q, join, terms)
	}
}