试图将两个表 linq 连接到 Sql

Question

我有以下表格：

Table Name: console_details               Table Name: console_features
-------------------                         -----------------
| console_id      |                         |       id      |
-------------------                         -----------------
|console_name     |                         |     bluray    |
-------------------                         -----------------
|console_type     |                         |   harddrive   |
-------------------                         -----------------
|console_startdate|
-------------------

console_id 字段和 id 字段都共享相同的数据公共字段我想将这两个表从我的 linq 连接到 sql 查询并获取控制台的硬盘大小。我无法在 stackoverflow 上找到与此类似的另一个问题。那么有什么建议吗？

这是我的 linq 代码：

public IEnumerable<console_details> GetConsole(DateTime startDate, DateTime endDate)
{
    DataClasses1DataContext mydatabase = new DataClasses1DataContext();
    var results = from data in mydatabase.console_details
                  where data.console_startdate >= startDate &&
                        endDate >= data.console_startdate
                  select data;

    return results;
}

Answer 1

你可以试试这个：

DataClasses1DataContext mydatabase = new DataClasses1DataContext();
var results = from cd in mydatabase.console_details   
              join cf in mydatabase.console_features
              on cd.console_id equals cf.id
              where cd.console_startdate >= startDate && 
                    endDate >= cd.console_startdate
              select new { Name = cd.console_name, HardDriveSize = cf.harddrive };

通过上述查询，您可以得到一系列具有两个属性的匿名类型的对象

• Name，即控制台名称。
• HardDriveSize，这是硬盘的大小。

更新

首先，我们必须声明一个具有我们需要的所有属性的类型。我将这种类型称为ConsoleView。您可以随意调用它，但您必须在以下代码中进行相应的更改。

public class ConsoleView
{
    // console_id
    public int Id { get; set; }

    // console_name
    public string Name { get; set; }

    // console_type
    public string ConsoleType {get; set; }

    // console_startdate
    public DateTime StartDate { get; set; }

    // harddrive
    public int HardDrive { get; set; }
}

我假设harddrive 的类型是int，console_type 的类型是string。 如果不是这样，您必须相应地更改它们。

那么你的方法应该改成下面这样：

public IEnumerable<ConsoleView> GetConsole(DateTime startDate, DateTime endDate)
{
    DataClasses1DataContext mydatabase = new DataClasses1DataContext();

    IEnumerable<ConsoleView> results = from cd in mydatabase.console_details   
                                       join cf in mydatabase.console_features
                                       on cd.console_id equals cf.id
                                       where cd.console_startdate >= startDate && 
                                       endDate >= cd.console_startdate
                                       select new ConsoleView
                                       {
                                           Id = cd.console_id, 
                                           Name = cd.console_name, 
                                           ConsoleType = cd.console_type,
                                           StartDate = cd.console_startdate,
                                           HardDriveSize = cf.harddrive 
                                       };

    return results;
}

更新 #2

我从您在 cmets 上发布的错误中了解到，您的数据上下文存在问题。所以，如果已经为访问console_details而构建了DataClasses1DataContext，并且为访问console_features而构建了DataClasses2DataContext，那么您必须将方法中的代码更改为以下代码：

public IEnumerable<ConsoleView> GetConsole(DateTime startDate, DateTime endDate)
{
    DataClasses1DataContext mydatabase1 = new DataClasses1DataContext();
    DataClasses2DataContext mydatabase2 = new DataClasses2DataContext();

    IEnumerable<ConsoleView> results = from cd in mydatabase1.console_details   
                                       join cf in mydatabase2.console_features
                                       on cd.console_id equals cf.id
                                       where cd.console_startdate >= startDate && 
                                       endDate >= cd.console_startdate
                                       select new ConsoleView
                                       {
                                           Id = cd.console_id, 
                                           Name = cd.console_name, 
                                           ConsoleType = cd.console_type,
                                           StartDate = cd.console_startdate,
                                           HardDriveSize = cf.harddrive 
                                       };

    return results;
}

Answer 2

为简单起见，我在查询中忽略了您的 startdate 和 enddate 变量。 因为我没有你的数据，你也没有提供 sampledata，所以我使用 Linq-to-Objects 而不是 Linq-to-SQL 创建了一个测试用例：

有 2 个类代表您的表格：

public class console_details
{
    public int Id { get; set; }
    public string console_name { get; set; }
    public string console_type { get; set; }
}

public class console_features
{
    public int Id { get; set; }
    public double blueray { get; set; }
    public double Harddrive { get; set; }
}

示例数据如下所示：

var consoleList = new List<console_details>()
{
    new console_details() {Id = 1, console_name = "Ps4", console_type ="Next-Gen"},
    new console_details() {Id = 2, console_name = "XB1", console_type ="Next-Gen"}
};

var featuresList = new List<console_features>()
{
    new console_features() {Id = 1, blueray = 23.9, Harddrive = 100},
    new console_features() {Id = 2, blueray = 30, Harddrive = 150}
};

最后但同样重要的是，我创建了一个 ViewModel 类来强输入结果：

public class ConsoleViewModel
{
    public int Id { get; set; }
    public string Name { get; set; }
    public double HardDrive { get; set; }
}

这样查询和输出看起来像这样：

var joinedResults = from con in consoleList
                    join feat in featuresList on con.Id equals feat.Id
                    select new ConsoleViewModel
                    {
                        Id = con.Id,
                        Name = con.console_name,
                        HardDrive = feat.Harddrive
                    };

使用这个，你的方法应该看起来像这样：

public IEnumerable<ConsoleViewModel> GetConsole(DateTime startDate, DateTime endDate)
{
    DataClasses1DataContext mydatabase = new DataClasses1DataContext();
    var results = from data in mydatabase.console_details
                  join feat in mydatabase.console features on data.Id equals feat.Id
                  where data.console_startdate >= startDate
                        && endDate >= data.console_startdate
                  select new ConsoleViewModel
                    {
                        Id = con.Id,
                        Name = con.console_name,
                        HardDrive = feat.Harddrive
                    };
    return results;
}