Dapper 中多重映射的正确使用

使用Dapper进行数据库操作是一种轻量级的ORM框架，它提供了高性能和简洁的API。在实际开发中，我们常常需要执行多重映射操作，即将多个表的数据映射到一个对象中。本文将介绍Dapper中多重映射的正确使用方法，并通过案例代码进行演示。

csharp
CREATE TABLE Author (
    Id INT PRIMARY KEY,
    Name NVARCHAR(50)
)
CREATE TABLE Book (
    Id INT PRIMARY KEY,
    Title NVARCHAR(100),
    AuthorId INT,
    FOREIGN KEY (AuthorId) REFERENCES Author (Id)
)

csharp
public class Author
{
    public int Id { get; set; }
    public string Name { get; set; }
    public List Books { get; set; }
}
public class Book
{
    public int Id { get; set; }
    public string Title { get; set; }
    public int AuthorId { get; set; }
}

csharp
using (var connection = new SqlConnection(connectionString))
{
    connection.Open();
    var sql = @"
        SELECT a.Id, a.Name, b.Id, b.Title, b.AuthorId
        FROM Author a
        JOIN Book b ON a.Id = b.AuthorId
        WHERE a.Id = @AuthorId";
    var result = connection.Query(
        sql,
        (author, book) =>
        {
            author.Books = author.Books ?? new List();
            author.Books.Add(book);
            return author;
        },
        splitOn: "Id",
        param: new { AuthorId = 1 },
        commandType: CommandType.Text,
        buffered: true);
    var author = result.FirstOrDefault();
    connection.Close();
}