Dapper Extension: class with composite fields, mapped to an individual table

Question

I have the following classes:

public class Publication
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string Headline { get; set; }
    public DateTime Published { get; set; }
    public ProductContact Contact { get; set; }
}

public class ProductContact
{
    public string FullName { get; set; }
    public string JobTitle { get; set; }
    public string Email { get; set; }
}

And the table associated with this structure, "Publications", has all these fields (included the properties of ProductContact).

If I try to insert a Publication row (with the ProductContact information included) the program throws an exception:

System.NotSupportedException: The member Contact of type ProductContact cannot be used as a parameter value

So, I added a mapper to map out the ProductContact properties to fields in the Properties table:

  public PublicationMapper ()
    {
        TableName = "Publications";

        Map(x => x.Contact.FullName).Column("ContactFullName");
        Map(x => x.Contact.JobTitle).Column("ContactJobTitle");
        Map(x => x.Contact.Email).Column("ContactEmail");

        AutoMap();
    }

With this mapper I get the same exception.

Then, I added the ignore statement for the Contact field, to tell Dapper to not include this element in the insert statement

            Map(x => x.Contact).Ignore();

In this case, I get another exception:

System.Data.SqlClient.SqlException (0x80131904): Must declare the scalar variable "@FullName".

It indicates that Dapper is ignoring completely this property, and the mapping added in the previous step does not have effect.

Is there a way to map out the ProductContact properties to the table fields?

Thank you.

Why not just an anonymous class `new { pub.Id, pub.Title,......, ContactFullName = pub.Contact.FullName, ContactJobTitle = pub.Contact.JobTitle,ContactEmail = pub.Contact.Email}`? Though it sounds like `ContactFullName` should actually just be `FullName` to match up with the parameter name in your SQL. Showing the SQL and the full Dapper call would also help here. — juharr, Jul 06 '16 at 18:29
It's unfortunate that it can't/won't do that. Found myself in the exact spot, trying to show management that Dapper is the way to go to help reduce code and ease-of-use. Especially when objects and their data counterparts have different names. Ah well — zerohero, Aug 02 '17 at 10:08

score 2 · Accepted Answer · answered Jul 07 '16 at 08:01

I don't think that this is possible with DapperExtensions.

In one of their issues, they say

Currently, we aren't planning to support nested objects. However, you can create your own Mapper that will allow for skipping over the nested object

I have tried a variety of approaches and different mapping classes and can't get anywhere - I don't think that they support any way to map nested property values and to ignore the property itself (which, if not done, will result in "cannot be used as a parameter value" error).

One approach would be to manually flatten your object into an anonymous class (as suggested by @juharr in a comment on your question), another approach would be to use something like AutoMapper to flatten your complex object into a flattened insert model.

Dapper Extension: class with composite fields, mapped to an individual table

1 Answers1