我有一个非常简单的测试项目,我试图弄清楚如何将子项添加到父项的集合中。
数据模型非常基础:
预期的/所需的
我预计结果只有一个有两个孩子的条目
GROUP1 - > {USER_1,USER_2}
GROUP类
public class GROUP
{
public GROUP()
{
this.USERs = new HashSet<USER>();
}
public int Group_ID { get; set; }
public string Name { get; set; }
public string Location { get; set; }
public ICollection<USER> USERs { get; set; }
}
USER类
public class USER
{
public int User_ID { get; set; }
public int Group_ID { get; set; }
public string Name { get; set; }
public Nullable<int> Age { get; set; }
public GROUP GROUP { get; set; }
}
小巧玲珑的方法
public GROUP Get(int id)
{
string sqlGetGroupExtended = $"SELECT _group.Group_ID, _group.Name, _group.Location, _user.User_ID, _user.Name, _user.GROUP_ID, _user.Age FROM dbo.[GROUP] _group " +
"LEFT JOIN dbo.[USER] _user ON _group.Group_ID = _user.Group_ID " +
"WHERE _group.Group_ID = @groupid;";
GROUP result = null;
var lookup = new Dictionary<int, GROUP>();
using (var connection = new SqlConnection(Properties.Settings.Default.CodeTest_DB))
{
var extendedGroup = connection.Query<GROUP, USER, GROUP>(sqlGetGroupExtended, (parent, child) =>
{
if (!lookup.TryGetValue(parent.Group_ID, out GROUP found))
{
lookup.Add(parent.Group_ID, found = parent);
}
found.USERs.Add(child);
return found;
}, param: new { groupid = id }, splitOn: "Location");
// result = extendedGroup <--- WHAT TO DO HERE?
}
return result;
}
我怎样才能做到这一点?
参考文献:
http://dapper-tutorial.net/dapper https://github.com/StackExchange/Dapper/blob/master/Dapper.Tests/MultiMapTests.cs#L12
如果您使用的是SQL Server 2016或Azure SQL,则可以使用JSON来返回分层对象:
https://medium.com/dapper-net/one-to-many-mapping-with-dapper-55ae6a65cfd4
这是我在这个主题上写的一篇文章,以及源代码,它展示了如何优雅地解决问题。
我的坏,因为代码显示在这里https://github.com/StackExchange/Dapper/blob/master/Dapper.Tests/MultiMapTests.cs#L12
我错过了.Distinct()
var extendedGroup = connection.Query<GROUP, USER, GROUP>(sqlGetGroupExtended, (parent, child) =>
{
if (!lookup.TryGetValue(parent.Group_ID, out GROUP found))
{
lookup.Add(parent.Group_ID, found = parent);
}
found.USERs.Add(child);
return found;
}, param: new { groupid = id }, splitOn: "Location,User_ID").Distinct();