在EF上级联多对多关系上删除

Question

These are my tables:

Is there a standard way to apply the DELETE ON CASCADE between them ?

In one-to-many relationship I had no problem, but in this case I had to manually remove with a method written by me.

Answer 1

As you showed on the picture you have only two tables. It is not possible to set relationship between them as many-to-many (only if you will add new columns to this tables when new pairs will appear, but this is very bad practice). You should create third table, which will contain pairs of their primary keys. And at your migration you will be able to specify cascadeDelete to true between each of main tables and this third one. See below:

Models:

public class BugReport
{
    public BugReport()
    {
        dublicates = new HashSet<DublicateBugReport>();
    }        

    public int ID { get; set; }
    public virtual ICollection<DublicateBugReport> dublicates { get; set; }
}

public class DublicateBugReport
{
    public DublicateBugReport()
    {
        reports = new HashSet<BugReport>();
    }        

    public int ID { get; set; }
    public virtual ICollection<BugReport> reports { get; set; }
}

Piece of Migration:

    public override void Up()
    {
        CreateTable(
            "BugReports",
            c => new
                {
                    ID = c.Int(nullable: false, identity: true),
                })
            .PrimaryKey(t => t.ID)                ;

        CreateTable(
            "DublicateBugReports",
            c => new
                {
                    ID = c.Int(nullable: false, identity: true),
                })
            .PrimaryKey(t => t.ID)                ;

        CreateTable(
            "DublicateBugReportBugReports",
            c => new
                {
                    DublicateBugReport_ID = c.Int(nullable: false),
                    BugReport_ID = c.Int(nullable: false),
                })
            .PrimaryKey(t => new { t.DublicateBugReport_ID, t.BugReport_ID })                

            //pay attention! - cascadeDelete: true
            .ForeignKey("DublicateBugReports", t => t.DublicateBugReport_ID, cascadeDelete: true)
            .ForeignKey("BugReports", t => t.BugReport_ID, cascadeDelete: true)
            .Index(t => t.DublicateBugReport_ID)
            .Index(t => t.BugReport_ID);

    }