包含路径表达式必须引用定义的导航属性

【问题标题】：The Include path expression must refer to a navigation property defined包含路径表达式必须引用定义的导航属性
【发布时间】：2019-05-21 06:08:16
【问题描述】：

我正在尝试创建一个通用包含，但我收到此错误。怎么了？谢谢。

包含路径表达式必须引用导航属性在类型上定义。使用虚线路径进行参考导航属性和用于集合导航的 Select 运算符属性。

_repository.FindWithIncludes(..., new List<...>
    {
        x => x.Property1,
        x => x.Property2,
    });   

 public ICollection<TEntity> FindWithIncludes(Expression<Func<TEntity, bool>> currentExpression, List<Expression<Func<TEntity, object>>> propertiesToInclude)
    {
        using (var customContext = new TContext())
        {
            return customContext.Set<TEntity>().Include(x => propertiesToInclude.Select(currentProperty => currentProperty)).Where(currentExpression).ToList();
        }
    }

【问题讨论】：

标签： c# entity-framework entity-framework-6 .net-4.7.2

【解决方案1】：

Include不能这样使用：

.Include(x => propertiesToInclude.Select(currentProperty => currentProperty)

您需要的是相当于为列表的每个表达式调用Include：

.Include(x => x.Property1)
.Include(x => x.Property2)
...
.Include(x => x.PropertyN)

可以通过如下代码实现：

var query = customContext.Set<TEntity>().AsQueryable();
foreach (var property in propertiesToInclude)
    query = query.Include(property); 
return query.Where(currentExpression).ToList();

或与使用Aggregate 方法相同：

return propertiesToInclude
    .Aggregate(customContext.Set<TEntity>().AsQueryable(), (q, p) => q.Include(p))
    .Where(currentExpression).ToList();

【讨论】：