Question

我的数据库中有两个表，如下所示：

enter image description here

我有这堂课：

   class Ean
   {
        public string Code{ get; set; }
   }

   class Article
   {
        public int Id { get; set; }
        public string Name { get; set; }
        public List<Ean> BarCode { get; set; }
   }

List<Article> arts = new List<Article>();

我创建了一个文章列表，并使用 dapper 进行查询。我想用文章的名称填写此列表，还要列出相关的 ean 文章列表。我尝试做这个查询：

SELECT ART.ID AS ID, ART.NAME AS NAME,EAN.EAN AS BARCODE
FROM ART,EAN
WHERE ART.ID = EAN.ID_ART;

并在c＃..

arts = conn.Query<Article>(query, null, transaction).ToList();

但不起作用。我该怎么办？谢谢..任何建议都是受欢迎的。

Answer 1

查看Dapper的Multi-Mapping功能。

Dapper允许您将单行映射到多个对象。这是一个关键功能，如果你想避免无关的查询和急切负载关联。

示例：

var sql = 
@"select * from #Posts p 
left join #Users u on u.Id = p.OwnerId 
Order by p.Id";

var data = connection.Query<Post, User, Post>(sql, (post, user) => { post.Owner = user; return post;});
var post = data.First();

post.Content.IsEqualTo("Sams Post1");
post.Id.IsEqualTo(1);
post.Owner.Name.IsEqualTo("Sam");
post.Owner.Id.IsEqualTo(99);

重要提示Dapper假设您的Id列名为“Id”或“id”，如果您的主键不同或者您想要拆分宽键除“Id”以外的行，使用可选的'splitOn'参数。

Answer 2

试试这个，我会这么认真

arts = conn.Query<Article>(query).ToList();

您还需要更改查询，如下所示。

SELECT ART.ID AS [Id], ART.NAME AS [Name],EAN.EAN AS [BarCode] 
FROM ART,EAN
WHERE ART.ID = EAN.ID_ART;

Answer 3

另一个解决方案，只需使用一个请求，只需两行代码，并且可以链接连接（例如三个表）：

为每个域对象覆盖Equals和GetHashCode（这可以通过继承自动执行）
添加两个扩展名以影响子行的父行

请求：

var data = connection.Query<Table1, Table2, Table3, Table3>(
        @"  SELECT * FROM Table1
        LEFT JOIN Table2 ON Table1.Id = Table1Id
        LEFT JOIN Table3 ON Table2.Id = Table2Id
        WHERE Table1.Id IN @Ids",
    (t1, t2, t3) => { t2.Table1 = t1; t3.Table2 = t2; return t3; },
    param: new { Ids = new int[] { 1, 2, 3 });

var read = data.GroupBy(t => t.Table2).DoItForEachGroup(gr => gr.Key.Table3s.AddRange(gr)).Select(gr => gr.Key).
    GroupBy(t => t.Table1).DoItForEachGroup(gr => gr.Key.Table2s.AddRange(gr)).Select(gr => gr.Key);

域对象：

public class Table1
{
    public Table1()
    {
        Table2s = new List<Table2>();
    }

    public Guid Id { get; set; }
    public IList<Table2> Table2s { get; private set; }

    public override bool Equals(object obj)
    {
        if (obj as Table1 == null) throw new ArgumentException("obj is null or isn't a Table1", "obj");
        return this.Id == ((Table1)obj).Id;
    }

    public override int GetHashCode()
    {
        return this.Id.GetHashCode();
    }
}

public class Table2
{
    public Table2()
    {
        Table3s = new List<Table3>();
    }

    public Guid Id { get; set; }
    public Guid Table1Id
    {
        get
        {
            if (Table1 == null)
                return default(Guid);
            return Table1.Id;
        }
    }
    public IList<Table3> Table3s { get; private set; }
    public Table1 Table1 { get; set; }

    public override bool Equals(object obj)
    {
        if (obj as Table2 == null) throw new ArgumentException("obj is null or isn't a Table2", "obj");
        return this.Id == ((Table2)obj).Id;
    }

    public override int GetHashCode()
    {
        return this.Id.GetHashCode();
    }
}

public class Table3
{
    public Table3()
    {

    }

    public Guid Id { get; set; }

    public Guid Table2Id
    {
        get
        {
            if (Table2 == null)
                return default(Guid);
            return Table2.Id;
        }
    }
    public Table2 Table2 { get; set; }

    public override bool Equals(object obj)
    {
        if (obj as Table3 == null) throw new ArgumentException("obj is null or isn't a Table3", "obj");
        return this.Id == ((Table3)obj).Id;
    }

    public override int GetHashCode()
    {
        return this.Id.GetHashCode();
    }
}

扩展程序：

public static class CollectionExtensions
{
    public static void AddRange<T>(this IList<T> that, IEnumerable<T> collection)
    {
        if (that == null)
            throw new ArgumentNullException("that", "that is null.");
        if (collection == null)
            throw new ArgumentNullException("collection", "collection is null.");

        if (that is List<T>)
        {
            ((List<T>)that).AddRange(collection);
            return;
        }

        foreach (T item in collection)
            that.Add(item);
    }

    public static IEnumerable<IGrouping<TKey, TElem>> DoItForEachGroup<TKey, TElem>(this IEnumerable<IGrouping<TKey, TElem>> group, Action<IGrouping<TKey, TElem>> action)
    {
        if (group == null)
            throw new ArgumentNullException("group", "group is null.");
        if (action == null)
            throw new ArgumentNullException("action", "action is null.");

        group.ToList().ForEach(gr => action(gr));
        return group;
    }
}

使用dapper c＃填充列表对象

3 个答案: