fix: add ON DELETE CASCADE for foreign keys (#585)

Spanner now supports ON DELETE CASCADE actions for foreign keys. This was however
not included in the generated migration script is this had been specified in the
model or migration.

Fixes #583

Author: olavloite

Google.Cloud.EntityFrameworkCore.Spanner.Tests/MigrationTests/GenerateCreateScriptTest.cs

@@ -138,7 +138,7 @@ public void Generate_Create_Script()
     `StartTime` TIMESTAMP NOT NULL,
     `SingerId` INT64 NOT NULL,
     `Title` STRING(200),
- CONSTRAINT `FK_Concerts_Singers` FOREIGN KEY (`SingerId`) REFERENCES `Singers` (`SingerId`),
+ CONSTRAINT `FK_Concerts_Singers` FOREIGN KEY (`SingerId`) REFERENCES `Singers` (`SingerId`) ON DELETE CASCADE,
  CONSTRAINT `FK_Concerts_Venues` FOREIGN KEY (`VenueCode`) REFERENCES `Venues` (`Code`),
 )PRIMARY KEY (`VenueCode`, `StartTime`, `SingerId`)
 
@@ -248,7 +248,7 @@ public void GenerateCreateScriptWithAutoIncrement()
     `StartTime` TIMESTAMP NOT NULL,
     `SingerId` INT64 NOT NULL,
     `Title` STRING(200),
- CONSTRAINT `FK_Concerts_Singers` FOREIGN KEY (`SingerId`) REFERENCES `Singers` (`SingerId`),
+ CONSTRAINT `FK_Concerts_Singers` FOREIGN KEY (`SingerId`) REFERENCES `Singers` (`SingerId`) ON DELETE CASCADE,
  CONSTRAINT `FK_Concerts_Venues` FOREIGN KEY (`VenueCode`) REFERENCES `Venues` (`Code`),
 )PRIMARY KEY (`VenueCode`, `StartTime`, `SingerId`)
 
@@ -358,7 +358,7 @@ public void GenerateCreateScriptWithIdentityColumnsDisabled()
     `StartTime` TIMESTAMP NOT NULL,
     `SingerId` INT64 NOT NULL,
     `Title` STRING(200),
- CONSTRAINT `FK_Concerts_Singers` FOREIGN KEY (`SingerId`) REFERENCES `Singers` (`SingerId`),
+ CONSTRAINT `FK_Concerts_Singers` FOREIGN KEY (`SingerId`) REFERENCES `Singers` (`SingerId`) ON DELETE CASCADE,
  CONSTRAINT `FK_Concerts_Venues` FOREIGN KEY (`VenueCode`) REFERENCES `Venues` (`Code`),
 )PRIMARY KEY (`VenueCode`, `StartTime`, `SingerId`)
 

Google.Cloud.EntityFrameworkCore.Spanner.Tests/MigrationTests/Migrations/20210309110233_Initial.cs

@@ -131,7 +131,7 @@ protected override void Up(MigrationBuilder migrationBuilder)
                         column: x => x.SingerId,
                         principalTable: "Singers",
                         principalColumn: "SingerId",
-                        onDelete: ReferentialAction.Restrict);
+                        onDelete: ReferentialAction.Cascade);
                     table.ForeignKey(
                         name: "FK_Concerts_Venues",
                         column: x => x.VenueCode,

Google.Cloud.EntityFrameworkCore.Spanner.Tests/MigrationTests/Models/SpannerMigrationSampleDbContext.cs

@@ -74,7 +74,7 @@ protected override void OnModelCreating(ModelBuilder modelBuilder)
                 entity.HasOne(d => d.Singer)
                     .WithMany(p => p.Concerts)
                     .HasForeignKey(d => d.SingerId)
-                    .OnDelete(DeleteBehavior.ClientSetNull)
+                    .OnDelete(DeleteBehavior.Cascade)
                     .HasConstraintName("FK_Concerts_Singers");
 
                 entity.HasOne(d => d.VenueCodeNavigation)

Google.Cloud.EntityFrameworkCore.Spanner.Tests/Migrations/SpannerMigrationSqlGeneratorTest.cs

@@ -248,7 +248,7 @@ public virtual void AddColumnOperation_with_defaultValue()
         public override void AddForeignKeyOperation_with_name()
         {
             base.AddForeignKeyOperation_with_name();
-            AssertSql(@"ALTER TABLE `Album` ADD  CONSTRAINT `FK_Album_Singer` FOREIGN KEY (`SingerId`) REFERENCES `Singer` (`SingerId`)
+            AssertSql(@"ALTER TABLE `Album` ADD  CONSTRAINT `FK_Album_Singer` FOREIGN KEY (`SingerId`) REFERENCES `Singer` (`SingerId`) ON DELETE CASCADE
 ");
         }
 

Google.Cloud.EntityFrameworkCore.Spanner/Migrations/SpannerMigrationsSqlGenerator.cs

@@ -320,6 +320,10 @@ protected override void ForeignKeyConstraint(
                 .Append(" (")
                 .Append(ColumnList(operation.PrincipalColumns))
                 .Append(")");
+            if (operation.OnDelete == ReferentialAction.Cascade)
+            {
+                builder.Append(" ON DELETE CASCADE");
+            }
         }
 
         private static string GetCorrectedColumnType(string columnType, int? maxLength)