使用 Dapper 在自定义 Poco 对象中返回模型

Question

我正在使用以下查询聚合数据：

var result = Connection.Query<TransactionStatsByUserGrouped>(
    @"SELECT usr.*, st.Amount, st.Count
    FROM Users usr
    RIGHT JOIN (select UserId, sum(Amount) as Amount, sum(Count) Count
        FROM (
            SELECT User2Id as UserId, sum(Amount) as Amount, count(TransactionId) Count
            FROM Transactions
            WHERE User1Id = @UserId
            GROUP BY User2Id
    ) t GROUP BY UserId) st
    ON st.UserId = usr.UserId
    ORDER BY st.Amount DESC",
    param: new { UserId = userId },
    transaction: Transaction
);

自定义 Poco 对象具有以下结构：

public class TransactionStatsByUserGrouped
{
    public User User { get; set; }
    public decimal Amount { get; set; }
    public int Count { get; set; }
}

其中 User 是一个实际的数据模型，包含以下属性：

public class User
{
    public string UserId { get; set; }
    public string Email { get; set; }
    public int Role { get; set; }
    public string Password { get; set; }
    // ...
}

我遇到的问题是我在 TransactionStatsByUserGrouped class:

中得到 User 模型的 null 结果

[
    {
        "user": null,
        "amount": 400.00,
        "count": 2
    },
    {
        "user": null,
        "amount": 100.00,
        "count": 1
    }
]

问题似乎在于，自定义 TransactionStatsByUserGrouped class 将模型用作属性，而不是将所有模型的属性列为单独的属性在 TransactionStatsByUserGrouped class 中。有解决办法吗？我不想手动映射每个 User 模型属性。

我想 return 用户的所有属性 + 每个用户的聚合统计信息 - 所有这些都在一个查询中。

使用

.Net Core 2 + Dapper + MySQL 连接器 (MariaDB)

Answer 1

根据文档你可以试试Multi Mapping

var sql = 
  @"SELECT usr.*, st.Amount, st.Count
    FROM Users usr
    RIGHT JOIN (select UserId, sum(Amount) as Amount, sum(Count) Count
        FROM (
            SELECT User2Id as UserId, sum(Amount) as Amount, count(TransactionId) Count
            FROM Transactions
            WHERE User1Id = @UserId
            GROUP BY User2Id
    ) t GROUP BY UserId) st
    ON st.UserId = usr.UserId
    ORDER BY st.Amount DESC";

var result = Connection.Query<TransactionStatsByUserGrouped, User, TransactionStatsByUserGrouped>(
    sql,
    (group, user) => { group.User = user; return group;},
    param: new { UserId = userId },
    transaction: Transaction
);

使用 Dapper 在自定义 Poco 对象中返回模型

Returning model in a custom Poco object using Dapper

c#

mysql

dapper

.net-core