Improve CrudModel code quality

tests/integration/fixtures/schema.sql

@@ -31,3 +31,30 @@ CREATE TABLE grid_nopk (
     y text
 );
 INSERT INTO grid_nopk (x, y) VALUES (1, 'a'), (2, 'b');
+
+CREATE TABLE crud_item (
+    id serial PRIMARY KEY,
+    name text NOT NULL,
+    qty integer,
+    flag boolean,
+    born date,
+    tag text DEFAULT 'dflt'
+);
+INSERT INTO crud_item (name, qty, flag, born) VALUES
+    ('a', 1, true, '2020-01-02'),
+    ('b', 2, false, NULL),
+    ('c', NULL, NULL, '2021-03-04'),
+    ('d', 4, true, NULL),
+    ('e', 5, false, NULL);
+
+CREATE TABLE crud_empty (
+    id serial PRIMARY KEY,
+    v text
+);
+
+CREATE TABLE crud_gen (
+    id integer GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
+    a integer,
+    b integer GENERATED ALWAYS AS (a * 2) STORED
+);
+INSERT INTO crud_gen (a) VALUES (1), (2);