cgen, checker: add panic in ORM for invalid queries, when there are no or {} blocks, add type checking for the fkey attribute, add tests (#16977)

vlib/orm/orm_insert_test.v

@@ -0,0 +1,87 @@
+import db.sqlite
+
+struct Parent {
+	id       int     [primary; sql: serial]
+	name     string
+	children []Child [fkey: 'parent_id']
+	notes    []Note  [fkey: 'owner_id']
+}
+
+struct Child {
+mut:
+	id        int    [primary; sql: serial]
+	parent_id int
+	name      string
+}
+
+struct Note {
+mut:
+	id       int    [primary; sql: serial]
+	owner_id int
+	text     string
+}
+
+fn test_orm_insert_with_multiple_child_elements() {
+	mut db := sqlite.connect(':memory:') or { panic(err) }
+
+	sql db {
+		create table Parent
+	}
+	sql db {
+		create table Child
+	}
+	sql db {
+		create table Note
+	}
+
+	new_parent := Parent{
+		name: 'test'
+		children: [
+			Child{
+				name: 'Lisa'
+			},
+			Child{
+				name: 'Steve'
+			},
+		]
+		notes: [
+			Note{
+				text: 'First note'
+			},
+			Note{
+				text: 'Second note'
+			},
+			Note{
+				text: 'Third note'
+			},
+		]
+	}
+
+	sql db {
+		insert new_parent into Parent
+	}
+
+	parent := sql db {
+		select from Parent where id == 1
+	}
+
+	assert parent.children.len == new_parent.children.len
+	assert parent.notes.len == new_parent.notes.len
+
+	children_count := sql db {
+		select count from Child
+	}
+	assert children_count == new_parent.children.len
+
+	note_count := sql db {
+		select count from Note
+	}
+	assert note_count == new_parent.notes.len
+
+	assert parent.children[0].name == 'Lisa'
+	assert parent.children[1].name == 'Steve'
+
+	assert parent.notes[0].text == 'First note'
+	assert parent.notes[1].text == 'Second note'
+	assert parent.notes[2].text == 'Third note'
+}