表'UsageSummaries'上的多态与引入FOREIGN KEY约束可能会导致循环或多个级联路径

Question

I have a following entity set (code sample is simplified, I left only the key & navigation properties below, and removed all data-holding properties)

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

    public virtual ICollection<ProgramUsageSummary> UsageSummaries { get; set; } = new List<ProgramUsageSummary>();
    public virtual ICollection<Function> Functions { get; set; } = new List<Function>();
}

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

        public virtual ICollection<FunctionUsageSummary> UsageSummaries { get; set; } = new List<FunctionUsageSummary>();
}

public class ProgramUsageSummary : UsageSummary
{
    public int ProgramId { get; set; }
    public Program Program { get; set; }

    public virtual ICollection<UsageDetail> UsageDetails { get; set; } = new List<UsageDetail>();
}

public class FunctionUsageSummary : UsageSummary
{
        public int FunctionId { get; set; }
        public Function Function { get; set; }

        public virtual ICollection<UsageDetail> UsageDetails { get; set; } = new List<UsageDetail>();
}

public class UsageDetail
{
        public int Id { get; set; }
        public virtual UsageSummary UsageSummary { get; set; }
        public int UsageSummaryId { get; set; }
}

public abstract class UsageSummary
{
    public int Id { get; set;}
}

A Program can have zero or many ProgramUsageSummaries .

Each of the ProgramUsageSummaries can have one or many UsageDetails .

A Program can also have zero or many Functions , each of which can have zero or many FunctionUsageSummaries , and each of those will have one or more UsageDetails .

With that setup, I am getting the following error:

Introducing FOREIGN KEY constraint 'FK_dbo.UsageSummaries_dbo.Programs_ProgramId' on table 'UsageSummaries' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints

How can I keep the polymorphic design (of UsageSummary ) and get rid of this error?

Answer 1

The most straightforward change is to configure the DbContext to not cascade deletes on multiple access paths. You will just have handle theis in code, eg to delete the FuntionSummaries in before deleting a Function, etc.

The other way is to remove the abstract base class UsageSummary from your DbContext. Then the database mapping for the different UsageSummary subtypes will be to separate and unrelated tables.