From ab663abb9ce04227aaeddf8e39eb3bd2b6100c97 Mon Sep 17 00:00:00 2001
From: Shay Rojansky <roji@roji.org>
Date: Sat, 29 Aug 2020 18:30:47 +0300
Subject: [PATCH] Handle transition from SERIAL to IDENTITY in idempotent
 migrations

Fixes #1157
---
 .../NpgsqlMigrationsSqlGenerator.cs           |  5 ++-
 .../NpgsqlMigrationsSqlGeneratorTest.cs       | 41 +++++++++++++++++++
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/src/EFCore.PG/Migrations/NpgsqlMigrationsSqlGenerator.cs b/src/EFCore.PG/Migrations/NpgsqlMigrationsSqlGenerator.cs
index b68799855..3e96d255f 100644
--- a/src/EFCore.PG/Migrations/NpgsqlMigrationsSqlGenerator.cs
+++ b/src/EFCore.PG/Migrations/NpgsqlMigrationsSqlGenerator.cs
@@ -405,7 +405,10 @@ protected override void Generate(AlterColumnOperation operation, IModel model, M
                             .AppendLine($"ALTER SEQUENCE {sequence} RENAME TO {oldSequenceWithoutSchema};")
                             .AppendLine($"{alterBase}DROP DEFAULT;")
                             .AppendLine($"{alterBase}ADD GENERATED {identityTypeClause} AS IDENTITY;")
-                            .AppendLine($"SELECT * FROM setval('{sequence}', nextval('{oldSequence}'), false);")
+                            // When generating idempotent scripts, migration DDL is enclosed in anonymous DO blocks,
+                            // where PERFORM must be used instead of SELECT
+                            .Append(Options.HasFlag(MigrationsSqlGenerationOptions.Idempotent) ? "PERFORM" : "SELECT")
+                            .AppendLine($" * FROM setval('{sequence}', nextval('{oldSequence}'), false);")
                             .AppendLine($"DROP SEQUENCE {oldSequence};");
                         break;
                     default:
diff --git a/test/EFCore.PG.Tests/Migrations/NpgsqlMigrationsSqlGeneratorTest.cs b/test/EFCore.PG.Tests/Migrations/NpgsqlMigrationsSqlGeneratorTest.cs
index aa56bf91a..daa08f842 100644
--- a/test/EFCore.PG.Tests/Migrations/NpgsqlMigrationsSqlGeneratorTest.cs
+++ b/test/EFCore.PG.Tests/Migrations/NpgsqlMigrationsSqlGeneratorTest.cs
@@ -4,6 +4,7 @@
 using Microsoft.EntityFrameworkCore.Diagnostics;
 using Microsoft.EntityFrameworkCore.Infrastructure;
 using Microsoft.EntityFrameworkCore.Metadata;
+using Microsoft.EntityFrameworkCore.Migrations;
 using Microsoft.EntityFrameworkCore.Migrations.Operations;
 using Microsoft.Extensions.DependencyInjection;
 using Npgsql.EntityFrameworkCore.PostgreSQL.Infrastructure;
@@ -425,6 +426,46 @@ public void CreateIndexOperation_collation()
 ");
         }
 
+        [Theory]
+        [InlineData(MigrationsSqlGenerationOptions.Default)]
+        [InlineData(MigrationsSqlGenerationOptions.Idempotent)]
+        public void Alter_column_change_serial_to_identity_idempotent(MigrationsSqlGenerationOptions options)
+        {
+            Generate(
+                modelBuilder => modelBuilder.Entity<Person>().Property<int>("Id").UseSerialColumn(),
+                new[]
+                {
+                    new AlterColumnOperation
+                    {
+                        Table = "Person",
+                        Name = "Id",
+                        ClrType = typeof(int),
+                        [NpgsqlAnnotationNames.ValueGenerationStrategy] =
+                            NpgsqlValueGenerationStrategy.IdentityByDefaultColumn,
+
+                        OldColumn = new AddColumnOperation
+                        {
+                            Table = "Person",
+                            Name = "Id",
+                            ClrType = typeof(int),
+                            [NpgsqlAnnotationNames.ValueGenerationStrategy] =
+                                NpgsqlValueGenerationStrategy.SerialColumn,
+                        }
+                    }
+                },
+                options);
+
+            AssertSql(
+                $@"ALTER TABLE ""Person"" ALTER COLUMN ""Id"" TYPE integer;
+ALTER TABLE ""Person"" ALTER COLUMN ""Id"" SET NOT NULL;
+ALTER SEQUENCE ""Person_Id_seq"" RENAME TO ""Person_Id_old_seq"";
+ALTER TABLE ""Person"" ALTER COLUMN ""Id"" DROP DEFAULT;
+ALTER TABLE ""Person"" ALTER COLUMN ""Id"" ADD GENERATED BY DEFAULT AS IDENTITY;
+{(options == MigrationsSqlGenerationOptions.Idempotent ? "PERFORM" : "SELECT")} * FROM setval('""Person_Id_seq""', nextval('""Person_Id_old_seq""'), false);
+DROP SEQUENCE ""Person_Id_old_seq"";
+");
+        }
+
         #region CockroachDB interleave-in-parent
 
         // Note that we don't run tests against actual CockroachDB instances, so these are unit tests asserting on SQL