我有这门课......
public class MyDTO
{
public int Id { get; set; }
public bool Selected { get; set; }
}
然后使用dapper尝试创建这样的列表......
var list = this.db.OpenConnection().Query<MyDTO>(
@"SELECT T1.id, T2.id IS NOT NULL AS selected
FROM table1 T1
LEFT
JOIN table2 T2
ON T2.id = T1.id
AND Tl.id = @Id",
new { Id = id });
返回像这样的结果集....
id selected
9 0
10 1
11 1
12 0
但是当执行上面的代码时,我收到错误
[InvalidCastException: Specified cast is not valid.]
Deserialize3d3c9260-abcb-4964-97c1-4a4e66b786d3(IDataReader ) +354
[DataException: Error parsing column 2 (selected=0 - Int64)]
Dapper.SqlMapper.ThrowDataException(Exception ex, Int32 index, IDataReader reader) in C:\Projects\Web\SqlMapper.cs:1685
Deserialize3d3c9260-abcb-4964-97c1-4a4e66b786d3(IDataReader ) +432
Dapper.<QueryInternal>d__13`1.MoveNext() in C:\Projects\Web\Source\SqlMapper.cs:608
System.Collections.Generic.List`1..ctor(IEnumerable`1 collection) +327
System.Linq.Enumerable.ToList(IEnumerable`1 source) +58
Dapper.SqlMapper.Query(IDbConnection cnn, String sql, Object param, IDbTransaction transaction, Boolean buffered, Nullable`1 commandTimeout, Nullable`1 commandType) in C:\Projects\Web\Source\SqlMapper.cs:538
我现在打算创建一个“翻译”属性,但这是一个不寻常的用例吗?
答案 0 :(得分:14)
我不确定这是否是最好的方法,但应该可以解决这个问题:
SELECT T1.id, CAST(CASE WHEN T2.id IS NULL THEN 0 ELSE 1 END AS BIT) AS selected
FROM ...
(说实话,我不相信你的T2.id IS NOT NULL AS selected
条款首先是合法的T-SQL,但是如果你说它正在运作那么我会接受你的话!)< / p>