Mapping entity in Dapper

问题:

I've just started working with Dapper and I don't seem to find something very simple like mapping an entity to a table in my database:

I have a stored procedure:

CREATE PROCEDURE [dbo].GetUserById (@UserId int)
AS  
begin               
        SELECT UserId,LastName,FirstName,EmailAddress
        FROM users
        WHERE UserID = @UserId

end
go

Then an entity:

public class User
{
    public int Id { get; set; }
    public string LastName { get; set; }
    public string FirstName { get; set; }
    public string Email { get; set; }
}

And a dapper query in my code:

int userid=1;
    User User = connection.Query<User>("#GetUserById", new {userid=userid}, commandType: CommandType.StoredProcedure).FirstOrDefault();

My question is: How can I tell my entity User that Id is Userid on my database?

In EF I would do something like this:

MapSingleType(c => new
            {
                UserId = c.Id,
                Firstname = c.Firstname,
                Lastname = c.Lastname,
                EmailAddress = c.Email
            }).ToTable("users");

How can the above be achieved in dapper?

回答1:

Dapper deliberately doesn't have a mapping layer; it is the absolute minimum that can work, and frankly covers the majority of real scenarios in the process. However, if I understand correctly that you don't want to alias in the TSQL, and don't want any pass-thru properties - then use the non-generic Query API:

User user = connection.Query("...", ...).Select(obj => new User {
           Id = (int) obj.UserId,
           FirstName = (string) obj.FirstName,
           LastName = (string) obj.LastName,
           Email = (string) obj.EmailAddress
        }).FirstOrDefault();

or perhaps more simply in the case of a single record:

var obj = connection.Query("...", ...).FirstOrDefault();
User user = new User {
      Id = (int) obj.UserId,
      FirstName = (string) obj.FirstName,
      LastName = (string) obj.LastName,
      Email = (string) obj.EmailAddress
};

The trick here is that the non-generic Query(...) API uses dynamic, offering up members per column name.

回答2:

It can't, your user class must be defined to match the result coming back from the query.

Once you've got the result back you must map it manually to another class (or use AutoMapper)

回答3:

You could try something like this:

public class User
{
    public int Id { get; set; }
    public string LastName { get; set; }
    public string FirstName { get; set; }
    public string Email { get; set; }

    #region Remappings

    public int UserId
    {
        get { return Id; }
        set { Id = value; }
    }

    #endregion
}

It might be overkill for your example, but I've found it useful in some situations to avoid cluttering every Query<> call with the remapping code.

回答4:

I would recommend NReco to you. It is performant like dapper but with easy mapping with attributes. nreco