How to set up a Composite Primary Key in a Dependent Entity using a Composite Primary Key from the Principal Entity in Entity Framework Core?

Question

How to set up a Composite Primary Key in a Dependent Entity using a Composite Primary Key from the Principal Entity in Entity Framework Core?

Goverdhan Jayaram 40

CPK-Departments

Wenbin Geng 741 Microsoft External Staff

When using efcore, use composite primary keys to represent entities. Many people will recommend it.

[Key("",Order)]

This method is implemented, but errors will be reported to a large extent.

"the entity type '' has multiple properties with the [Key] attribute. Composite primary keys can only be set using 'HasKEey' in 'OnModelCreating'"

You can use custom attributes, here is an example:

[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter, AllowMultiple = false, Inherited = true)]
    public class CompositeKeysAttribute : Attribute
    {
        private string name;
        public int Order;

        public CompositeKeysAttribute(string name)
        {
            this.name = name;
            Order = 1;
        } 
    }
}

Set key in OnModelCreating:

  void AdKeyAction(ModelBuilder modelBuilder)
        {
            foreach (var mutableEntityType in modelBuilder.Model.GetEntityTypes())
            {  
                if (mutableEntityType.ClrType == null)
                    continue;
                var files = mutableEntityType.ClrType.GetMembers().Where(c=>c.CustomAttributes.Any(c=>c.AttributeType==typeof(CompositeKeysAttribute))); 
                var properties = new List<string>();
                foreach (var f in files)
                {
                    properties.Add(f.Name); 
                }
                if (properties.Count > 0)
                {
                    modelBuilder.Entity(mutableEntityType.ClrType).HasKey(properties.ToArray()); 
                } 
            }
        }

When using:

public class User
{
   [CompositeKeys("UserName",Order=1)] 

    public string UserName{set;get;} 
  [CompositeKeys("UserArea",Order=2)] 
  public string UserArea{get;set;} 
}

Your answer

Wenbin Geng 741 Reputation points Microsoft External Staff

2024-01-15T02:44:27.57+00:00

When using efcore, use composite primary keys to represent entities. Many people will recommend it.

[Key("",Order)]

This method is implemented, but errors will be reported to a large extent.

"the entity type '' has multiple properties with the [Key] attribute. Composite primary keys can only be set using 'HasKEey' in 'OnModelCreating'"

You can use custom attributes, here is an example:

[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter, AllowMultiple = false, Inherited = true)] public class CompositeKeysAttribute : Attribute { private string name; public int Order; public CompositeKeysAttribute(string name) { this.name = name; Order = 1; } } }

Set key in OnModelCreating:

void AdKeyAction(ModelBuilder modelBuilder) { foreach (var mutableEntityType in modelBuilder.Model.GetEntityTypes()) { if (mutableEntityType.ClrType == null) continue; var files = mutableEntityType.ClrType.GetMembers().Where(c=>c.CustomAttributes.Any(c=>c.AttributeType==typeof(CompositeKeysAttribute))); var properties = new List<string>(); foreach (var f in files) { properties.Add(f.Name); } if (properties.Count > 0) { modelBuilder.Entity(mutableEntityType.ClrType).HasKey(properties.ToArray()); } } }

When using:

public class User { [CompositeKeys("UserName",Order=1)] public string UserName{set;get;} [CompositeKeys("UserArea",Order=2)] public string UserArea{get;set;} }

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How to set up a Composite Primary Key in a Dependent Entity using a Composite Primary Key from the Principal Entity in Entity Framework Core?

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