关联已有数据的多对多表问题

问题描述

大家好，



我正在尝试使用attach方法将两个多表联系起来（组和学生）。但是，这不能通过使用以下代码来实现：

Hi all,

I am trying to use the attach method to relate two many to many tables (Group and Student). However, this is not working by making use of the following code:

using (var db = new ManyToManyContainer())
{
   //get existing learner
   var existingStudent = (from s in db.Students
         where s.RegNo== "X1"
         select s).FirstOrDefault<Student>();

   //Get existing group
   var existingGroup = (from g in db.Groups
         where g.GroupName == "G1"
         select g).FirstOrDefault<Group>();

   existingStudent.Groups.Attach(existingGroup);
   db.SaveChanges();
}

找不到Attach方法并给出错误：



System.Collections.Generic.ICollection< ManyToManyAttatch.Group>'不包含'Attach'的定义，也没有扩展方法'Attach'接受a可以找到类型'System.Collections.Generic.ICollection< ManyToManyAttatch.Group>'的第一个参数（您是否缺少using指令或汇编引用？）



以下是VS用于创建表的SQL脚本。

The Attach method is not found and gives the error:

System.Collections.Generic.ICollection<ManyToManyAttatch.Group>' does not contain a definition for 'Attach' and no extension method 'Attach' accepting a first argument of type 'System.Collections.Generic.ICollection<ManyToManyAttatch.Group>' could be found (are you missing a using directive or an assembly reference?)

Below is my SQL Script that VS is using to create the tables.

-- Creating table 'Students'
CREATE TABLE [dbo].[Students] (
    [StudentId] int IDENTITY(1,1) NOT NULL,
    [RegNo] nvarchar(max)  NOT NULL,
    [Name] nvarchar(max)  NOT NULL
);
GO

-- Creating table 'Groups'
CREATE TABLE [dbo].[Groups] (
    [GroupId] int IDENTITY(1,1) NOT NULL,
    [GroupName] nvarchar(max)  NOT NULL,
    [GroupSize] int  NOT NULL
);
GO

-- Creating table 'StudentGroup'
CREATE TABLE [dbo].[StudentGroup] (
    [Students_StudentId] int  NOT NULL,
    [Groups_GroupId] int  NOT NULL
);
GO

-- --------------------------------------------------
-- Creating all PRIMARY KEY constraints
-- --------------------------------------------------

-- Creating primary key on [StudentId] in table 'Students'
ALTER TABLE [dbo].[Students]
ADD CONSTRAINT [PK_Students]
    PRIMARY KEY CLUSTERED ([StudentId] ASC);
GO

-- Creating primary key on [GroupId] in table 'Groups'
ALTER TABLE [dbo].[Groups]
ADD CONSTRAINT [PK_Groups]
    PRIMARY KEY CLUSTERED ([GroupId] ASC);
GO

-- Creating primary key on [Students_StudentId], [Groups_GroupId] in table 'StudentGroup'
ALTER TABLE [dbo].[StudentGroup]
ADD CONSTRAINT [PK_StudentGroup]
    PRIMARY KEY CLUSTERED ([Students_StudentId], [Groups_GroupId] ASC);
GO

-- --------------------------------------------------
-- Creating all FOREIGN KEY constraints
-- --------------------------------------------------

-- Creating foreign key on [Students_StudentId] in table 'StudentGroup'
ALTER TABLE [dbo].[StudentGroup]
ADD CONSTRAINT [FK_StudentGroup_Student]
    FOREIGN KEY ([Students_StudentId])
    REFERENCES [dbo].[Students]
        ([StudentId])
    ON DELETE NO ACTION ON UPDATE NO ACTION;
GO

-- Creating foreign key on [Groups_GroupId] in table 'StudentGroup'
ALTER TABLE [dbo].[StudentGroup]
ADD CONSTRAINT [FK_StudentGroup_Group]
    FOREIGN KEY ([Groups_GroupId])
    REFERENCES [dbo].[Groups]
        ([GroupId])
    ON DELETE NO ACTION ON UPDATE NO ACTION;

-- Creating non-clustered index for FOREIGN KEY 'FK_StudentGroup_Group'
CREATE INDEX [IX_FK_StudentGroup_Group]
ON [dbo].[StudentGroup]
    ([Groups_GroupId]);
GO

我完全陷入困境。请帮忙。

I am totally stuck. Please assist.

推荐答案

using (var db = new ManyToManyContainer())
                {
                    //get existing learner
                    var existingStudent = (from s in db.Students
                                           where s.RegNo == "X1"
                                           select s).FirstOrDefault<Student>();
                    //Get existing group

                    var existingGroup = (from g in db.Groups
                                         where g.GroupName == "G1"
                                         select g).FirstOrDefault<Group>();

                    existingStudent.Groups.Add(existingGroup);

                    db.SaveChanges();

                    success = true;

谢谢一切都一样。

Thanks all the same.

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