Online not null constraints: SET NOT NULL

README.md

@@ -45,6 +45,7 @@ $ pg-schema-diff plan --dsn "postgres://postgres:postgres@localhost:5432/postgre
   * Online index replacement: If some index is changed, the new version will be built before the old version is dropped, preventing a window where no index is backing queries
   * Online check constraint builds: Check constraints are added as `INVALID` before being validated, eliminating the need
 	for a long access-exclusive lock on the table
+  * Online `ALTER ... SET NOT NULL` using check constraints to eliminate the need for an access-exclusive lock on the table
   * Prioritized index builds: Building new indexes is always prioritized over deleting old indexes
 * A comprehensive set of features to ensure the safety of planned migrations:
   * Operators warned of dangerous operations.

go.mod

@@ -7,6 +7,7 @@ require (
 	github.com/google/uuid v1.3.0
 	github.com/jackc/pgx/v4 v4.14.0
 	github.com/kr/pretty v0.3.1
+	github.com/lib/pq v1.10.2
 	github.com/manifoldco/promptui v0.9.0
 	github.com/mitchellh/hashstructure/v2 v2.0.2
 	github.com/spf13/cobra v1.7.0

internal/migration_acceptance_tests/acceptance_test.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"testing"
 
+	"github.com/google/uuid"
 	_ "github.com/jackc/pgx/v4/stdlib"
 	"github.com/kr/pretty"
 	"github.com/stretchr/testify/suite"
@@ -42,6 +43,10 @@ type (
 		oldSchemaDDL []string
 		newSchemaDDL []string
 
+		// ddl is used to assert the exact DDL (of the statements) that  generated. This is useful when asserting
+		// exactly how a migration is performed
+		ddl []string
+
 		// expectedHazardTypes should contain all the unique migration hazard types that are expected to be within the
 		// generated plan
 		expectedHazardTypes []diff.MigrationHazardType
@@ -86,6 +91,8 @@ func (suite *acceptanceTestSuite) runTestCases(acceptanceTestCases []acceptanceT
 }
 
 func (suite *acceptanceTestSuite) runSubtest(tc acceptanceTestCase, expects expectations, planOpts []diff.PlanOpt) {
+	uuid.SetRand(&deterministicRandReader{})
+
 	// normalize the subtest
 	if expects.outputState == nil {
 		expects.outputState = tc.newSchemaDDL
@@ -145,6 +152,14 @@ func (suite *acceptanceTestSuite) runSubtest(tc acceptanceTestCase, expects expe
 	newDbDump := suite.directlyRunDDLAndGetDump(expects.outputState)
 	suite.Equal(newDbDump, oldDbDump, prettySprintPlan(plan))
 
+	if tc.ddl != nil {
+		var generatedDDL []string
+		for _, stmt := range plan.Statements {
+			generatedDDL = append(generatedDDL, stmt.DDL)
+		}
+		suite.Equal(tc.ddl, generatedDDL)
+	}
+
 	// Make sure no diff is found if we try to regenerate a plan
 	plan, err = diff.GeneratePlan(context.Background(), oldDbConn, tempDbFactory, tc.newSchemaDDL, planOpts...)
 	suite.Require().NoError(err)
@@ -204,6 +219,18 @@ func prettySprintPlan(plan diff.Plan) string {
 	return fmt.Sprintf("%# v", pretty.Formatter(plan.Statements))
 }
 
+type deterministicRandReader struct {
+	counter int8
+}
+
+func (r *deterministicRandReader) Read(p []byte) (int, error) {
+	for i := 0; i < len(p); i++ {
+		p[i] = byte(r.counter)
+		r.counter++
+	}
+	return len(p), nil
+}
+
 func TestAcceptanceSuite(t *testing.T) {
 	suite.Run(t, new(acceptanceTestSuite))
 }

internal/migration_acceptance_tests/check_constraint_cases_test.go

@@ -149,6 +149,29 @@ var checkConstraintCases = []acceptanceTestCase{
 			`,
 		},
 	},
+	{
+		name: "Add check constraint and change data type",
+		oldSchemaDDL: []string{
+			`
+			CREATE TABLE foobar(
+			    id INT PRIMARY KEY,
+				foo VARCHAR(255)
+			);
+			`,
+		},
+		newSchemaDDL: []string{
+			`
+			CREATE TABLE foobar(
+			    id INT PRIMARY KEY,
+				foo INT CHECK ( foo > 0 )
+			);
+			`,
+		},
+		expectedHazardTypes: []diff.MigrationHazardType{
+			diff.MigrationHazardTypeAcquiresAccessExclusiveLock,
+			diff.MigrationHazardTypeImpactsDatabasePerformance,
+		},
+	},
 	{
 		name: "Add check constraint with quoted identifiers",
 		oldSchemaDDL: []string{
@@ -258,6 +281,31 @@ var checkConstraintCases = []acceptanceTestCase{
 			`,
 		},
 	},
+	{
+		name: "Drop check constraint and change data type",
+		oldSchemaDDL: []string{
+			`
+			CREATE TABLE foobar(
+			    "ID" INT PRIMARY KEY,
+				foo VARCHAR(255),
+				"Bar" BIGINT CHECK ( "Bar" > 0 )
+			);
+			`,
+		},
+		newSchemaDDL: []string{
+			`
+			CREATE TABLE foobar(
+			    "ID" INT PRIMARY KEY,
+				foo VARCHAR(255),
+			   	"Bar" TEXT
+			);
+			`,
+		},
+		expectedHazardTypes: []diff.MigrationHazardType{
+			diff.MigrationHazardTypeAcquiresAccessExclusiveLock,
+			diff.MigrationHazardTypeImpactsDatabasePerformance,
+		},
+	},
 	{
 		name: "Drop column with check constraints",
 		oldSchemaDDL: []string{