Dapper映射抛出无效的转换

Question

Two tables:

+-Person-+       +--Rank--+
| Id     |       | Id     |
| FName  |       | Name   |
| LName  |       +--------+
| Rank   |
+--------+

The object model looks the exact same except Rank in Person is of type RankModel instead of int.

I do a simple inner join on them:

string sql = "SELECT pe.Id, pe.LName, pe.FName, pe.Rank, ra.Id, ra.Name" +
             "FROM Person pe INNER JOIN Rank ra ON ra.Id = pe.Rank";

Then I use Dapper to map:

return connection.Query<PersonModel, RankModel, PersonModel>(sql, (per, rank) =>
    {
    per.Rank = rank;
    return per;
    }).ToList();

But I get an exception:

InvalidCastException: Invalid cast from 'System.Int16' to 'MainDB.Models.RankModel'.

Clearly it's trying to cast an int to a RankModel, but I can't figure out why -- it should be splitting the return into two objects and then attaching the RankModel object into the Rank property of the PersonModel object. This is driving me crazy, I've spent 3 hours on this and can't figure out what's going on.

Answer 1

You need to add 'splitOn' param in query statement in order to split them into Person, Rank model objects.

Also your sql needs to be refactored as below

string sql = "SELECT pe.Id, pe.LName, pe.FName, ra.Id, ra.Name" +
             "FROM Person pe INNER JOIN Rank ra ON ra.Id = pe.Rank";

And your statement should be

return connection.Query<PersonModel, RankModel, PersonModel>(sql, (per, rank) =>
    {
    per.Rank = rank;
    return per;
    }, splitOn:"Id,Id").ToList();