Don't generate both IDENTITY and NULL in migrations (#1849)

Fixes #1848

Author: roji

src/EFCore.PG/Migrations/NpgsqlMigrationsSqlGenerator.cs

@@ -1419,12 +1419,16 @@ protected override void ColumnDefinition(
                     .Append(DelimitIdentifier(collation));
             }
 
-            builder.Append(operation.IsNullable ? " NULL" : " NOT NULL");
-
-            DefaultValue(operation.DefaultValue, operation.DefaultValueSql, columnType, builder);
-
             if (valueGenerationStrategy.IsIdentity())
+            {
                 IdentityDefinition(operation, builder);
+            }
+            else
+            {
+                builder.Append(operation.IsNullable ? " NULL" : " NOT NULL");
+
+                DefaultValue(operation.DefaultValue, operation.DefaultValueSql, columnType, builder);
+            }
         }
 
         // Note: this definition is only used for creating new identity columns, not for alterations.

test/EFCore.PG.FunctionalTests/Migrations/MigrationsNpgsqlTest.cs

@@ -150,7 +150,7 @@ await Test(
 
             AssertSql(
                 @"CREATE TABLE ""People"" (
-    ""Id"" integer NOT NULL GENERATED BY DEFAULT AS IDENTITY
+    ""Id"" integer GENERATED BY DEFAULT AS IDENTITY
 );");
         }
 
@@ -171,7 +171,7 @@ await Test(
 
             AssertSql(
                 @"CREATE TABLE ""People"" (
-    ""Id"" integer NOT NULL GENERATED ALWAYS AS IDENTITY
+    ""Id"" integer GENERATED ALWAYS AS IDENTITY
 );");
         }
 
@@ -199,7 +199,7 @@ await Test(
 
             AssertSql(
                 @"CREATE TABLE ""People"" (
-    ""Id"" integer NOT NULL GENERATED ALWAYS AS IDENTITY (START WITH 10 INCREMENT BY 2 MAXVALUE 2000)
+    ""Id"" integer GENERATED ALWAYS AS IDENTITY (START WITH 10 INCREMENT BY 2 MAXVALUE 2000)
 );");
         }
 
@@ -702,7 +702,7 @@ await Test(
                 });
 
             AssertSql(
-                @"ALTER TABLE ""People"" ADD ""SomeColumn"" integer NULL GENERATED BY DEFAULT AS IDENTITY;");
+                @"ALTER TABLE ""People"" ADD ""SomeColumn"" integer GENERATED BY DEFAULT AS IDENTITY;");
         }
 
         [Fact]
@@ -727,7 +727,7 @@ await Test(
                 });
 
             AssertSql(
-                @"ALTER TABLE ""People"" ADD ""SomeColumn"" integer NULL GENERATED ALWAYS AS IDENTITY;");
+                @"ALTER TABLE ""People"" ADD ""SomeColumn"" integer GENERATED ALWAYS AS IDENTITY;");
         }
 
         [Fact]
@@ -765,7 +765,7 @@ await Test(
                 });
 
             AssertSql(
-                @"ALTER TABLE ""People"" ADD ""SomeColumn"" integer NULL GENERATED BY DEFAULT AS IDENTITY (START WITH 5 INCREMENT BY 2 MINVALUE 3 MAXVALUE 2000 CYCLE CACHE 10);");
+                @"ALTER TABLE ""People"" ADD ""SomeColumn"" integer GENERATED BY DEFAULT AS IDENTITY (START WITH 5 INCREMENT BY 2 MINVALUE 3 MAXVALUE 2000 CYCLE CACHE 10);");
         }
 
         [Fact]
@@ -828,7 +828,7 @@ await Test(
                 });
 
             AssertSql(
-                @"ALTER TABLE ""People"" ADD ""SomeColumn"" integer NOT NULL GENERATED BY DEFAULT AS IDENTITY;");
+                @"ALTER TABLE ""People"" ADD ""SomeColumn"" integer GENERATED BY DEFAULT AS IDENTITY;");
         }
 
         [Fact]