Question

在我目前的项目中(实际上很小),有3个表/POCO实体,希望利用EF加以操纵。

表格如下:

Status (contains status details)
StatusStatusType (which is needed because of the many-2-many relationship)
StatusType (A table which is used to group statuses by type)

我现在想在数据库和用户代码中创造新的地位,如以下。

//Create new status (POCO) entity
var newStatus = new Status {
    StatusId = status.Id,
    UserId = user.Id,
    Text = status.text,
    CreateDate = DateTime.Now
};

// Persist need status to database
using (var db = new demoEntities())
{
    db.Statuses.AddObject(newStatus);
    db.SaveChanges();
}

该法典规定了罚款,但希望也设定地位实体的StatusType。所有可能的地位类型均已列入StatusType>/em>表。我不想创造新的地位,只是一个参考。

我用的是:

status.StatusTypes == "new";

Update 22-04-2012 13:31

例子简化,在解决办法范围内跨越多个项目。由于这一原因,在创建的章节(如意向)中不使用守则。然而,我确实知道科索沃警察部队需要参考的地位。

Answer 1

如果你知道你的地位已经存在,你现在也必须是你的首要任务。如果你具有主要关键价值,你可以采用这种办法:

var newStatus = new Status {
    StatusId = status.Id,
    UserId = user.Id,
    Text = status.text,
    CreateDate = DateTime.Now
};

// Just dummy object for existing status type
var existingStatusType = new StatusType {
    Id = existingStatusTypeId
};

// Persist need status to database
using (var db = new demoEntities())
{
    db.Statuses.AddObject(newStatus);
    // First let EF know that the status type already exists
    // Attaching prior to making relation is important!
    db.StatusTypes.Attach(existingStatusType);
    // Now make relation between new and existing entity 
    newStatus.StatusTypes.Add(existingStatusType);
    db.SaveChanges();
}

如果你不想在持久性守则中建立关系,那么你必须使用很少差别的方法。

var newStatus = new Status {
    StatusId = status.Id,
    UserId = user.Id,
    Text = status.text,
    CreateDate = DateTime.Now
};

// Just dummy object for existing status type
var existingStatusType = new StatusType {
    Id = existingStatusTypeId
};

newStatus.StatusTypes.Add(existingStatusType);

// Persist need status to database
using (var db = new demoEntities())
{
    // This will add both newStatus and existingStatusType as new entities
    db.Statuses.AddObject(newStatus);
    // You must fix it to make sure that existingStatusType is not inserted 
    // to database again
    status.StatusTypes.ForEach(st =>
        db.ObjectStateManager.ChangeObjectState(st, EntityState.Unchanged));
    db.SaveChanges();
}

Update 22-04-2012 13:31

友情链接