Introducing FOREIGN KEY constraint may cause cycles or multiple cascade paths - why?

Because Stage is required, all one-to-many relationships where Stage is involved will have cascading delete enabled by default. It means, if you delete a Stage entity

the delete will cascade directly to Side

the delete will cascade directly to Card and because Card and Side have a required one-to-many relationship with cascading delete enabled by default again it will then cascade from Card to Side

So, you have two cascading delete paths from Stage to Side - which causes the exception.

You must either make the Stage optional in at least one of the entities (i.e. remove the [Required] attribute from the Stage properties) or disable cascading delete with Fluent API (not possible with data annotations):

modelBuilder.Entity<Card>()
    .HasRequired(c => c.Stage)
    .WithMany()
    .WillCascadeOnDelete(false);

modelBuilder.Entity<Side>()
    .HasRequired(s => s.Stage)
    .WithMany()
    .WillCascadeOnDelete(false);

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I had a table that had a circular relationship with others and I was getting the same error. Turns out it is about the foreign key which was not nullable. If the key is not nullable the related object must be deleted, and circular relations don't allow that. So use nullable foreign key.

[ForeignKey("StageId")]
public virtual Stage Stage { get; set; }
public int? StageId { get; set; }

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Anybody wondering how to do it in EF core:

      protected override void OnModelCreating(ModelBuilder modelBuilder)
            {
                foreach (var relationship in modelBuilder.Model.GetEntityTypes().SelectMany(e => e.GetForeignKeys()))
                {
                    relationship.DeleteBehavior = DeleteBehavior.Restrict;
                }
           ..... rest of the code.....

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I was getting this error for lots of entities when I was migrating down from an EF7 model to an EF6 version. I didn't want to have to go through each entity one at a time, so I used:

builder.Conventions.Remove<ManyToManyCascadeDeleteConvention>();
builder.Conventions.Remove<OneToManyCascadeDeleteConvention>();

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You can set cascadeDelete to false or true (in your migration Up() method). Depends upon your requirement.

AddForeignKey("dbo.Stories", "StatusId", "dbo.Status", "StatusID", cascadeDelete: false);

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In .NET Core I changed the onDelete option to ReferencialAction.NoAction

         constraints: table =>
            {
                table.PrimaryKey("PK_Schedule", x => x.Id);
                table.ForeignKey(
                    name: "FK_Schedule_Teams_HomeId",
                    column: x => x.HomeId,
                    principalTable: "Teams",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.NoAction);
                table.ForeignKey(
                    name: "FK_Schedule_Teams_VisitorId",
                    column: x => x.VisitorId,
                    principalTable: "Teams",
                    principalColumn: "Id",
                    onDelete: ReferentialAction.NoAction);
            });

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I had this issue also, I solved it instantly with this answer from a similar thread

In my case, I didn't want to delete the dependent record on key deletion. If this is the case in your situation just simply change the Boolean value in the migration to false:

AddForeignKey("dbo.Stories", "StatusId", "dbo.Status", "StatusID", cascadeDelete: false);

Chances are, if you are creating relationships which throw this compiler error but DO want to maintain cascade delete; you have an issue with your relationships.

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I fixed this. When you add the migration, in the Up() method there will be a line like this:

.ForeignKey("dbo.Members", t => t.MemberId, cascadeDelete:True)

If you just delete the cascadeDelete from the end it will work.

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Just for documentation purpose, to someone that comes on the future, this thing can be solved as simple as this, and with this method, you could do a method that disabled one time, and you could access your method normally

Add this method to the context database class:

protected override void OnModelCreating(DbModelBuilder modelBuilder) {
    modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();
}

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In .NET Core I played with all upper answers - but without any success. I made changes a lot in DB structure and every time added new migration attempting to update-database, but received the same error.

Then I started to remove-migration one by one until Package Manager Console threw me exception:

The migration '20170827183131_***' has already been applied to the database

After that, I added new migration (add-migration) and update-database successfully

So my suggestion would be: clear out all your temp migrations, until your current DB state.

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public partial class recommended_books : DbMigration
{
    public override void Up()
    {
        CreateTable(
            "dbo.RecommendedBook",
            c => new
                {
                    RecommendedBookID = c.Int(nullable: false, identity: true),
                    CourseID = c.Int(nullable: false),
                    DepartmentID = c.Int(nullable: false),
                    Title = c.String(),
                    Author = c.String(),
                    PublicationDate = c.DateTime(nullable: false),
                })
            .PrimaryKey(t => t.RecommendedBookID)
            .ForeignKey("dbo.Course", t => t.CourseID, cascadeDelete: false) // was true on migration
            .ForeignKey("dbo.Department", t => t.DepartmentID, cascadeDelete: false) // was true on migration
            .Index(t => t.CourseID)
            .Index(t => t.DepartmentID);

    }

    public override void Down()
    {
        DropForeignKey("dbo.RecommendedBook", "DepartmentID", "dbo.Department");
        DropForeignKey("dbo.RecommendedBook", "CourseID", "dbo.Course");
        DropIndex("dbo.RecommendedBook", new[] { "DepartmentID" });
        DropIndex("dbo.RecommendedBook", new[] { "CourseID" });
        DropTable("dbo.RecommendedBook");
    }
}

When your migration fails you are given a couple of options: 'Introducing FOREIGN KEY constraint 'FK_dbo.RecommendedBook_dbo.Department_DepartmentID' on table 'RecommendedBook' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints. Could not create constraint or index. See previous errors.'

Here is an example of using the 'modify other FOREIGN KEY constraints' by setting 'cascadeDelete' to false in the migration file and then run 'update-database'.

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Make your Foreign key attributes nullable. That will work.

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This sounds weird and I don't know why, but in my case that was happening because my ConnectionString was using "." in "data source" attribute. Once I changed it to "localhost" it workded like a charm. No other change was needed.

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The existing answers are great I just wanted to add that I ran into this error because of a different reason. I wanted to create an Initial EF migration on an existing DB but I didn't use the -IgnoreChanges flag and applied the Update-Database command on an empty Database (also on the existing fails).

Instead I had to run this command when the current db structure is the current one:

Add-Migration Initial -IgnoreChanges

There is likely a real problem in the db structure but save the world one step at a time...

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In .NET 5 < and .NET Core 2.0 < you can use .OnDelete(DeleteBehavior.Restrict) in OnModelCreating like @Nexus23 answer but you do not need to disable cascade for every model.

Example with join entity type configuration many-to-many:

internal class MyContext : DbContext
{
    public MyContext(DbContextOptions<MyContext> options)
        : base(options)
    {
    }

    public DbSet<Post> Posts { get; set; }
    public DbSet<Tag> Tags { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Post>()
            .HasMany(p => p.Tags)
            .WithMany(p => p.Posts)
            .UsingEntity<PostTag>(
                j => j
                    .HasOne(pt => pt.Tag)
                    .WithMany(t => t.PostTags)
                    .HasForeignKey(pt => pt.TagId)
                    .OnDelete(DeleteBehavior.Restrict),
                j => j
                    .HasOne(pt => pt.Post)
                    .WithMany(p => p.PostTags)
                    .HasForeignKey(pt => pt.PostId)
                    .OnDelete(DeleteBehavior.Restrict),
                j =>
                {
                    j.Property(pt => pt.PublicationDate).HasDefaultValueSql("CURRENT_TIMESTAMP");
                    j.HasKey(t => new { t.PostId, t.TagId });
                });
    }
}

public class Post
{
    public int PostId { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }

    public ICollection<Tag> Tags { get; set; }
    public List<PostTag> PostTags { get; set; }
}

public class Tag
{
    public string TagId { get; set; }

    public ICollection<Post> Posts { get; set; }
    public List<PostTag> PostTags { get; set; }
}

public class PostTag
{
    public DateTime PublicationDate { get; set; }

    public int PostId { get; set; }
    public Post Post { get; set; }

    public string TagId { get; set; }
    public Tag Tag { get; set; }
}

Sources:

https://docs.microsoft.com/en-us/ef/core/modeling/relationships?tabs=fluent-api%2Cfluent-api-simple-key%2Csimple-key#join-entity-type-configuration

https://docs.microsoft.com/en-us/dotnet/api/microsoft.entityframeworkcore.deletebehavior?view=efcore-5.0

This does require you to remove the many to many relationship yourself or you will receive the following error when you remove a parent entity:

The association between entity types '' and '' has been severed, but the relationship is either marked as required or is implicitly required because the foreign key is not nullable. If the dependent/child entity should be deleted when a required relationship is severed, configure the relationship to use cascade deletes. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the key values

You can solve this by using DeleteBehavior.ClientCascade instead which will allow EF to perform cascade deletes on loaded entities.

internal class MyContext : DbContext
{
    public MyContext(DbContextOptions<MyContext> options)
        : base(options)
    {
    }

    public DbSet<Post> Posts { get; set; }
    public DbSet<Tag> Tags { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Post>()
            .HasMany(p => p.Tags)
            .WithMany(p => p.Posts)
            .UsingEntity<PostTag>(
                j => j
                    .HasOne(pt => pt.Tag)
                    .WithMany(t => t.PostTags)
                    .HasForeignKey(pt => pt.TagId)
                    .OnDelete(DeleteBehavior.Cascade),
                j => j
                    .HasOne(pt => pt.Post)
                    .WithMany(p => p.PostTags)
                    .HasForeignKey(pt => pt.PostId)
                    .OnDelete(DeleteBehavior.ClientCascade),
                j =>
                {
                    j.Property(pt => pt.PublicationDate).HasDefaultValueSql("CURRENT_TIMESTAMP");
                    j.HasKey(t => new { t.PostId, t.TagId });
                });
    }
}

public class Post
{
    public int PostId { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }

    public ICollection<Tag> Tags { get; set; }
    public List<PostTag> PostTags { get; set; }
}

public class Tag
{
    public string TagId { get; set; }

    public ICollection<Post> Posts { get; set; }
    public List<PostTag> PostTags { get; set; }
}

public class PostTag
{
    public DateTime PublicationDate { get; set; }

    public int PostId { get; set; }
    public Post Post { get; set; }

    public string TagId { get; set; }
    public Tag Tag { get; set; }
}

https://docs.microsoft.com/en-us/dotnet/api/microsoft.entityframeworkcore.deletebehavior?view=efcore-5.0

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None of the aforementioned solutions worked for me. What I had to do was use a nullable int (int?) on the foreign key that was not required (or not a not null column key) and then delete some of my migrations.

Start by deleting the migrations, then try the nullable int.

Problem was both a modification and model design. No code change was necessary.

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The simple way is to, Edit your migration file (cascadeDelete: true) into (cascadeDelete: false) then after assign the Update-Database command in your Package Manager Console.if it's problem with your last migration then all right. Otherwise check your earlier migration history, copy those things, paste into your last migration file, after that do it the same thing. it perfectly works for me.

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You could add this in your DataContext.cs, this works for me...

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();
    modelBuilder.Conventions.Remove<ManyToManyCascadeDeleteConvention>();
}

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I ran into the same problem and stuck for a long. The following steps saved me. Go through the constraints and change the onDelete ReferentialAction to NoAction from Cascade

  constraints: table =>
  {
      table.PrimaryKey("PK_table1", x => x.Id);
      table.ForeignKey(
         name: "FK_table1_table2_table2Id",
         column: x => x.table2Id,
         principalTable: "table2",
         principalColumn: "Id",
         onDelete: ReferentialAction.NoAction);
  });

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