Migrating existing many-to-many relationships to new implicit many-to-many relationships

[adnan-kamili]

We have many existing many-to-many relationships wherein we have created the join table to map the entities as was needed before efcore 5.0

So we had three entities User, Tag and UserTag. We changed this to use the new EFCore 5.0 way, but the new migrations created drop the existing join table and tries to create a new join table, which will cause data loss and all the existing relationships will be lost. We also removed the join table entry from DBContext:

public DbSet<UserTag> UserTags { get; set; }

Here is the migration code generated:

        protected override void Up(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.DropTable(
                name: "UserTags");

            migrationBuilder.CreateTable(
                name: "UserTag",
                columns: table => new
                {
                    UsersId = table.Column<string>(type: "text", nullable: false),
                    TagsId = table.Column<string>(type: "text", nullable: false)
                },
                constraints: table =>
                {
                    table.PrimaryKey("PK_UserTag", x => new { x.UsersId, x.TagsId });
                    table.ForeignKey(
                        name: "FK_UserTag_Users_LicensesId",
                        column: x => x.UsersId,
                        principalTable: "Users",
                        principalColumn: "Id",
                        onDelete: ReferentialAction.Cascade);
                    table.ForeignKey(
                        name: "FK_UserTag_Tags_TagsId",
                        column: x => x.TagsId,
                        principalTable: "Tags",
                        principalColumn: "Id",
                        onDelete: ReferentialAction.Cascade);
                });

            migrationBuilder.CreateIndex(
                name: "IX_UserTag_TagsId",
                table: "UserTag",
                column: "TagsId");
        }

EF Core version: 5.0.1
Database provider: Microsoft.EntityFrameworkCore.Npgsql
Target framework: .NET 5.0

[anranruye]

Obvious, the implicit join table name is UserTag which is different from UserTags. You should use explicit configuration to rename the join table name to UserTags. Or you can first rename the DbSet name UserTags to UserTag, add a new migration, then remove the DbSet.

[ajcvickers]

@adnan-kamili As @anangaur says, you will need to configure the many-to-many relationship to match your existing table and column names. See https://docs.microsoft.com/en-us/ef/core/modeling/relationships?tabs=fluent-api%2Cfluent-api-simple-key%2Csimple-key#many-to-many for more information.

[adnan-kamili]

Thanks, renaming the DbSet before migrating to the new method worked. Creating and adding tags on User entity works too by just adding the tag to the user.Tags collection.

But when I remove a tag from user.Tags it doesn't work (tag is not removed from the user). The tag remains there only. Previously removing UserTag from user.UserTags join table worked. The following code (using UserTags instead of Tags) worked when join table was used:

user.Tags.RemoveAll(t => !requestModel.Tags.Contains(t.Name));
context.Entry(user);
await context.SaveChangesAsync();

[ajcvickers]

@adnan-kamili Please attach a small, runnable project or post a small, runnable code listing that reproduces what you are seeing so that we can investigate.

[adnan-kamili]

I am not sure whether I will be able to provide one, but one additional info that may help is that I eager-load the user and user.Tags as no-tracking entities. Then attach user and user.tags for tracking. Then update the entities. The removed entities from user.Tags are not removed on SaveAsync().

[ajcvickers]

@adnan-kamili The documentation on how change tracking works might help you with this: https://docs.microsoft.com/en-us/ef/core/change-tracking/

[anranruye]

@adnan-kamili see #23787, this issue is already fixed by version 5.0.3 which is not released yet.

[adnan-kamili]

@anranruye I could see this was some bug, thanks for the issue link. For now, I had to revert to using join tables.

One more issue which I faced is that when loading user as no-tracking entity (with tags eager-loader), any update to the user causes a crash unless I attach user and user.tags both (when using context.Entry(entity).State = EntityState.Unchanged; for attaching, as we don't want to unnecessarily attach all children).

[ajcvickers]

@adnan-kamili While we try our best, we generally are not going to be able to give answers without seeing what your code is doing. Please attach a small, runnable project or post a small, runnable code listing that reproduces what you are seeing so that we can investigate.

[ajcvickers]

EF Team Triage: Closing this issue as the requested additional details have not been provided and we have been unable to reproduce it.

BTW this is a canned response and may have info or details that do not directly apply to this particular issue. While we'd like to spend the time to uniquely address every incoming issue, we get a lot traffic on the EF projects and that is not practical. To ensure we maximize the time we have to work on fixing bugs, implementing new features, etc. we use canned responses for common triage decisions.