Question

我想使用LINQ查询一些实体：

public class Link: Entity, IAggregateRoot
{
    public Guid RelationId { get; private set; }
    public Guid ConstructionId { get; private set; }

    public virtual Relation Relation { get; private set; }
    public virtual Construction Construction { get; private set; }

    private Link()
    {
    }
}

public class Relation: Entity, IAggregateRoot
{
    public string Number { get; private set; }
    public Guid PersonId { get; private set; }
    public Guid RelationTypeId { get; private set; }

    public virtual Person Person { get; private set; }
    public virtual RelationType RelationType { get; private set; }

    [NotMapped]
    public int ContextKey { get; set; }

    private Relation()
    {
    }
}

我有一个查询，该查询通过提供构造ID并使用Link实体来返回关系。该查询如下所示，并且可以正常工作：

public IQueryable<Relation> GetRelationsByConstructionId(Guid constructionId)
{
    var links base.Get(x => x.Construction.ConstructionId == constructionId);

    var relations = links.Include(x => x.Relation)
                         .Select(x => x.Relation)
                         .Include(x => x.Person)
                         .Include(x => x.RelationType);

    return relations;
}

在关系中，我有一个NotMapped元素ContextKey，我想在查询调用中设置此ContextKey（例如，我想将其设置为30）。基本上，我想做这样的事情来扩展我使用的查询：

public IQueryable<Relation> GetRelationsByConstructionId(Guid constructionId)
{
    var links base.Get(x => x.Construction.ConstructionId == constructionId);

    var relations = links.Include(x => x.Relation)
                         .Select(x => x.Relation)
                         .Include(x => x.Person)
                         .Include(x => x.RelationType);

    var updatedRelations = relations.ForEachAsync(x => x.ContextKey = 30);

    return updatedRelations;
}

这当然不起作用，因为在 ForEachAsync 之后， updatedRelations 的类型为 Task ，并且预期的返回类型必须为可查询的<关系> 。

如何使查询正常工作并以正确的 IQueryable 类型获取所需的输出？

Answer 1

这是我反对未映射属性的原因之一-它们不适合LINQ to Entities查询。

您可以使用以下LINQ to Objects技巧：

var updatedRelations = relations
    .AsEnumerable()
    .Select(x => { x.ContextKey = 30; return x; })
    .AsQueryable();

但请注意，这不是真正的EF Core可查询的，因此将在AsEnumerable()之前的查询具体化结果中在内存中执行进一步的操作，如过滤，排序，分页等。

Answer 2

我自己通过更新查询进行了如下修复：

public IQueryable<Relation> GetRelationsByConstructionId(Guid constructionId)
{
    var links base.Get(x => x.Construction.ConstructionId == constructionId);

    var relations = links.Include(x => x.Relation)
                     .Select(x => x.Relation)
                     .Include(x => x.Person)
                     .Include(x => x.RelationType);

    relations.ToList().ForEach(x => x.ContextKey = 30);

    return relations;
}

EF核心-LINQ-将属性分配给IQueryable <t>

2 个答案: