Ignore a property only on Update with Dapper?

Question

Setup

As part of my data access layer, I am using Dapper with DapperExtensions and representing my database entities with models. Some of these models contain fields used for logging or change tracking, like so:

public class ExampleClass : BaseModel, ITypeWithChangeTracking
{
    public int ExampleClassId { get { return Id; } set { Id = value; } }
    public DateTime CreatedDate { get; set; }
    public string CreatedBy { get; set; }

    // More properties
}

public class ExampleClassMapper : ClassMapper<ExampleClass>
{
    public ExampleClassMapper() : base()
    {
        Map(m => m.ExampleClassId).Key(KeyType.Identity);
        Map(m => m.Id).Ignore();
        base.AutoMap();
    }
}

In this example, BaseModel is an abstract class that specifies the model has some integer Id (to make it easier to work with generics); ITypeWithChangeTracking specifies it should have the change tracking fields. So far, I've been able to shuffle most of the DAL logic into a generic implementation that can be shared among all models, and I'd like to keep that up with those that implement change tracking.

Tools Used

C#

Dapper

DapperExtensions

Problem

Some of the change tracking fields should be set when an object is inserted, but not when it is updated. I'm having trouble implementing this in a generic way that can be reused for each model.

Question

Is there anything I can use with Dapper or DapperExtensions to specify that a field should be included for an Insert, but ignored for an Update?

I've looked at various attributes such as ReadOnly and Ignore for mappings, but so far everything I've found is a blanket "always include" or "always ignore". Preferably, I'd like this to work with the standard Update() function and not require a specialized sproc, though I'm not sure that's possible. Any loopholes or useful decorators I'm missing?

(Note: Major brownie points if there's a way to shuffle this specification all the way up to the ITypeWithChangeTracking interface!)

Edit:

Rather than create separate models, I tweaked the code that was already setting the change tracking values from ITypeWithChangeTracking so that it would recognize unset values (null, DateTime.Min, etc). It was already checking to see whether the record was new or previously existing, so I had it fetch relevant values from the existing record if 1) the record did exist and 2) the model had unset change tracking values.

score 2 · Answer 1 · answered Jul 26 '18 at 12:58

As I mentioned in comment, the way to go is to create separate class for UPDATE that does not include the property you want to ignore for UPDATE. You may not need to create the separate class every time; you may reuse your View Model or similar.

Other solution is to fall back to Dapper bypassing Dapper Extensions. With this, you have multiple options available now as Dapper is far more flexible. You may choose to pass anonymous object or dynamic param for updating only the properties you want to update.

Similar discussion is already done here and here.

Ignore a property only on Update with Dapper?

Setup

Tools Used

Problem

Question

1 Answers1