Question

我有以下几类人试图对实体表示反对:

public class ConsumerIndexItem: MappedViewModel<Consumer>
{
    public string UserName { get; set; }
    public string RoleDescription { get; set; }
    public override void MapFromEntity(Consumer entity)
    {
        base.MapFromEntity(entity);
        UserName = entity.User.UserName;
    }
}
public class Consumer: AuditableEntity
{
    public virtual User User { get; set; }
    public virtual Role Role { get; set; }
}
public class IndexModel<TIndexItem, TEntity> : ViewModel where TEntity : new()
{
    public IndexModel()
    {
        Items = new List<TIndexItem>();            
    } 
    public List<TIndexItem> Items { get; set; }
    public virtual void MapFromEntityList(IEnumerable<TEntity> entityList)
    {
        Items = Mapper.Map<IEnumerable<TEntity>, List<TIndexItem>>(entityList);
    }
}
public class ConsumerIndexModel: IndexModel<ConsumerIndexItem, Consumer>

然而,如果我用以下代码进行测绘:

var model = new ConsumerIndexModel();
var list = _repository.List().Where(c => c.Parent == null).ToList();
model.MapFromEntityList(list);
return View(model);

on the line UserName = entity.User.UserName; in ConsumerIndexItem I get the following exception:

A relationship multiplicity constraint violation occurred: An EntityReference can have no more than one related object, but the query returned more than one related object. This is a non-recoverable error.

如果我执行<代码>?entity。用户:UserName in the Immediate Window I获得预期用户名值。什么可能是错误的?

Answer 1

Let me explain why I had this exception and you may be able to correlate it with your own situation. I had EF Code First model mapped to the existing database. There was one-to-many relationship between two of the entities. The child table had composite primary consisting of the Id and Date. However, I missed the second segment of the primary key in my fluent map:

this.HasKey(t => t.Id);

其中一个奇怪之处是,该模式是行之有效的,但在某些情形下却成为例外,很难理解为什么。很明显,当欧洲武装部队装上儿童实体的母子时,有不止一名家长,因为钥匙不仅有伊德,而且有日期。这项决议将主要内容的第二部分列入:

this.HasKey(t => new { t.Id, t.Date });

The tool that helped me to pinpoint the problem was EF Power Tools, currently it is in Beta 3. The tool gives a context menu for the EF context class where one the item is View Entity Model DDL SQL. Although I could have found this just by checking the code, the tool is nice in showing how close the EF model matches the actual database.

我认为,你再次获得这一例外,因为出于某种原因,关系的多样性受到了侵犯。就我而言,这是不正确的绘图,因为你或许是别的东西,我可以参考你的代码。

Answer 2

我认为,问题可能是,你假定每个用户只有一个消费者,而在数据方面却不正确。

我也存在同样的问题,因为这种关系在不断发展,我把这种关系变成了一体。

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