在一个呼叫中从多个表中选择 [英] Select from multiple tables in one call

问题描述

在我的代码中，我有一个页面，其中包含来自3个不同表的信息.为了显示此信息，我进行了3次SQL select调用，并将它们组合在一个列表中，以作为Model传递到我的视图.我可以通过一个SQL调用来做到吗?数据之间没有任何联系.

In my code I have a page that includes information from 3 different tables. To show this information I make 3 SQL select calls and unite them in one list to pass as Model to my view. Can I do it with one SQL call? Data has no connection with one another.

我的代码:

public ActionResult Index()
{
    StorePageData PageData = new StorePageData();
    return View(PageData);
}
public class StorePageData
{
     public List<Table1Data> Table1 { get; set; }
     public List<Table2Data> Table2 { get; set; }
     public List<Table3Data> Table3 { get; set; }

     public StorePageData()
     {
          Table1  = //loading from Database1
          Table2  = //loading from Database2
          Table3  = //loading from Database3
     }
}
public class Table1Data
{
     public int Id { get; set; }
     public double Info1 { get; set; }
     public string Info2 { get; set; }
}
public class Table2Data
{
     public int Id { get; set; }
     public List<int> Info1 { get; set; }
     public List<int> Info2 { get; set; }
}
public class Table3Data
{
     public int Id { get; set; }
     public List<string> Info1 { get; set; }
     public List<string> Info2 { get; set; }
}

如果有一种方法可以在一个SQL请求中加载所有3个表，则将大大缩短此页面的加载时间.

If there is a way to load all 3 tables in one SQL request it will improve significantly the load time of this page.

谢谢.

推荐答案

您可以使用DataReader在单个请求中获得多个结果集.您可以在有或没有实体框架的情况下使用它.

You can get multiple result sets in a single request using a DataReader. You can use it with or without entity framework.

如果使用的是Entity Framework，则可以传递 ObjectContext.Translate 方法将多个结果集转换为请求的对象类型.用于创建数据读取器的命令可以是存储过程，也可以仅使用包含查询的命令来塑造多个结果集.

If you are using Entity Framework, you can pass a DbDataReader to ObjectContext.Translate method to translate multiple result set to requested object types. The command which is used to create the data reader can be a stored procedure, or you can simply use a command containing your queries to shape multiple result set.

示例

List<Table1> list1;
List<Table2> list2;

using (var cn = new SqlConnection(@"Connection String"))
{
    cn.Open();
    using (var cmd = cn.CreateCommand())
    {
        cmd.CommandText = "SELECT * FROM Table1; SELECT * FROM Table2";
        var reader = cmd.ExecuteReader(); 
        using (var db = new YourDbContext())
        {
            var context = ((IObjectContextAdapter)db).ObjectContext;
            list1 = context.Translate<Table1>(reader).ToList();
            reader.NextResult();
            list2 = context.Translate<Table2>(reader).ToList();
        }
    }
}

如果您使用的是

If you are using SqlDataAdapter, you can simply pass a command containing your queries and then using Fill, fill a data set. The data adapter itself will use DataReader behind the scene.

示例

var connectionString = @"Connection String";
var commandText = "SELECT * FROM Table1; SELECT * FROM Table2;";
var ds = new DataSet();
using (var da = new SqlDataAdapter(commandText, connectionString))
{
    da.Fill(ds);
}

然后，您可以将结果整形为List<Table1>和List<Table2>.

Then you can shape the results to List<Table1> and List<Table2>.

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