EF Core - dropping a column workaround (sqlite)

entity-framework-core sql sqlite

Question

It is documented and known that EF core migration scripts don't support dropping a column. So I'm trying to do it by hand.

My model classes are:

class Master
{
    public int Id { get; set; }
    public string ToBeDeleted { get; set; }
}

class Detail
{
    public int Id { get; set; }

    public Master Master { get; set; }
}

My context:

class Context : DbContext
{
    public DbSet<Master> Masters { get; set; }
    public DbSet<Detail> Details { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlite("Filename=local.db");
        base.OnConfiguring(optionsBuilder);
    }
}

I create a migration script then run the following program to create the db file and add a couple of rows:

class Program
{
    static void Main(string[] args)
    {
        using (var context = new Context())
        {
            context.Database.Migrate();
            if(!context.Masters.Any())
            {
                var master = new Master {ToBeDeleted = "Some string"};
                context.Add(master);
                context.Add(new Detail {Master = master});
                context.SaveChanges();
            }
        }
    }
}

I delete ToBeDeleted property of Master class and generated a second migration script, which generates the very simple code that doesn't work because it'll only be supported in the future:

protected override void Up(MigrationBuilder migrationBuilder)
{
    migrationBuilder.DropColumn(
        name: "ToBeDeleted",
        table: "Masters");
}

protected override void Down(MigrationBuilder migrationBuilder)
{
   migrationBuilder.AddColumn<string>(
        name: "ToBeDeleted",
        table: "Masters",
        nullable: true);
}

So it's time for me to write my own stuff, and this is what I've tried:

protected override void Up(MigrationBuilder migrationBuilder)
{
    migrationBuilder.Sql("PRAGMA foreign_keys=OFF");
    migrationBuilder.CreateTable(
        name: "NEW_Masters",
        columns: table => new
        {
             Id = table.Column<int>(nullable: false)
                .Annotation("Sqlite:Autoincrement", true),
        },
         constraints: table =>
         {
             table.PrimaryKey("PK_Masters", x => x.Id);
         });
    migrationBuilder.Sql("INSERT INTO NEW_Masters SELECT Id FROM Masters;");
    migrationBuilder.DropTable("Masters");
    migrationBuilder.RenameTable("NEW_Masters", newName: "Masters");
    migrationBuilder.Sql("PRAGMA foreign_keys=OFF");
}

However this causes the context.Database.Migrate() to throw an exception:

An unhandled exception of type 'Microsoft.Data.Sqlite.SqliteException' occurred in Microsoft.EntityFrameworkCore.Relational.dll

Additional information: SQLite Error 19: 'FOREIGN KEY constraint failed'.

Finally, the question: how do I drop a column by hand in the migration script?

UPDATE

Following advice I got on the discussion, I used Script-Migration to generate the sql from the migration scripts and got this:

CREATE TABLE IF NOT EXISTS "__EFMigrationsHistory" (
    "MigrationId" TEXT NOT NULL CONSTRAINT "PK___EFMigrationsHistory" PRIMARY KEY,
    "ProductVersion" TEXT NOT NULL
);

CREATE TABLE "Masters" (
    "Id" INTEGER NOT NULL CONSTRAINT "PK_Masters" PRIMARY KEY AUTOINCREMENT,
    "ToBeDeleted" TEXT
);

CREATE TABLE "Details" (
    "Id" INTEGER NOT NULL CONSTRAINT "PK_Details" PRIMARY KEY AUTOINCREMENT,
    "MasterId" INTEGER,
    CONSTRAINT "FK_Details_Masters_MasterId" FOREIGN KEY ("MasterId") REFERENCES "Masters" ("Id") ON DELETE RESTRICT
);

CREATE INDEX "IX_Details_MasterId" ON "Details" ("MasterId");

INSERT INTO "__EFMigrationsHistory" ("MigrationId", "ProductVersion")
VALUES ('20170127204056_Migration1', '1.1.0-rtm-22752');

INSERT INTO Masters (ToBeDeleted) VALUES ("ASDF"); --I've added this line manually for test only

INSERT INTO Details (MasterId) VALUES (1); --I've added this line manually for test only

PRAGMA foreign_keys="0";

CREATE TABLE "NEW_Masters" (
    "Id" INTEGER NOT NULL CONSTRAINT "PK_Masters" PRIMARY KEY AUTOINCREMENT
);

INSERT INTO NEW_Masters SELECT Id FROM Masters;;

DROP TABLE "Masters";

ALTER TABLE "NEW_Masters" RENAME TO "Masters";

PRAGMA foreign_keys="1";

INSERT INTO "__EFMigrationsHistory" ("MigrationId", "ProductVersion")
VALUES ('20170127204851_Migration2', '1.1.0-rtm-22752');

And the script works fine. The exception is some foreign key check performed by EF somewhere.

1
2
1/30/2017 3:00:26 PM

Accepted Answer

The EF core developers pointed out that PRAGMA foreign_keys=0 doesn't work within a transaction in SQLite, and it was suggested to use the migrationBuilder.Sql method to suppress the use of the transaction.

So I came up with:

    protected override void Up(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.CreateTable(
            name: "NEW_Masters",
            columns: table => new
            {
                Id = table.Column<int>(nullable: false)
                    .Annotation("Sqlite:Autoincrement", true),
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_Masters", x => x.Id);
            });
        migrationBuilder.Sql("INSERT INTO NEW_Masters SELECT Id FROM Masters;");
        migrationBuilder.Sql("PRAGMA foreign_keys=\"0\"", true);
        migrationBuilder.Sql("DROP TABLE Masters", true);
        migrationBuilder.Sql("ALTER TABLE NEW_Masters RENAME TO Masters", true);
        migrationBuilder.Sql("PRAGMA foreign_keys=\"1\"", true);
    }

And it does the trick.

3
1/30/2017 6:05:23 PM

Popular Answer

For the lazier what I did was manually delete the migrations in the solution and the sqlite db then added a migration. When that pesky error comes up that it cant drop, comment out the the body of the up method like so:in the generated script.Then update the db. worked fine for me when It generated a fk when I added the reference object type SocialMediaLinks to my users. This is not a suitable solution for all as it may cause data loss.ALSO DELETE THE CLASS ENTITY that was causing the fk dependencey.

//generated migration:

 protected override void Up(MigrationBuilder migrationBuilder)
        {
             //comment out--
            //migrationBuilder.DropColumn(
            //    name: "SocialMediaLinks",
            //    table: "ProfileUserVM");

            //migrationBuilder.DropColumn(
            //    name: "SocialMediaLinks",
            //    table: "AspUsers");
        }

        protected override void Down(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.AddColumn<string>(
                name: "SocialMediaLinks",
                table: "ProfileUserVM",
                nullable: true);

            migrationBuilder.AddColumn<string>(
                name: "SocialMediaLinks",
                table: "AspUsers",
                nullable: true);
        }


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