ef Core Table 关系包含计数错误

Question

我是 .NET 和 EF Core 的新手。我无法计算与 post table.

关联的 table

我想做的是显示 post 上的总点赞数。

PostManager:

var posts = await _unitOfWork.Posts
                             .GetAllAsync(p => p.UserId == userId && 
                                               p.IsActive == true, 
                                          l => l.Likes.Count());

EfBaseRepository:

public async Task<IList<TEntity>> GetAllAsync(Expression<Func<TEntity, bool>> predicate = null, params Expression<Func<TEntity, object>>[] includeProperties)
{
        IQueryable<TEntity> query = _context.Set<TEntity>();

        if (predicate != null)
        {
            query = query.Where(predicate);
        }

        if (includeProperties.Any())
        {
            foreach (var includeProperty in includeProperties)
            {
                query = query.Include(includeProperty);
            }
        }

        return await query.ToListAsync();
}

错误：

System.InvalidOperationException: The expression 'Convert(l.Likes.AsQueryable().Count(), Object)' is invalid inside an 'Include' operation, since it does not represent a property access: 't => t.MyProperty'. To target navigations declared on derived types, use casting ('t => ((Derived)t).MyProperty') or the 'as' operator ('t => (t as Derived).MyProperty'). Collection navigation access can be filtered by composing Where, OrderBy(Descending), ThenBy(Descending), Skip or Take operations. For more information on including related data, see http://go.microsoft.com/fwlink/?LinkID=746393.

Answer 1

改为这样做。基本上，您想实现“延迟加载”。在您的“GetAllAsync”方法中，“includeProperties”需要属性。在这种情况下，“喜欢”属性所以它是“l.Likes”而不是“l.Likes.Count()”。之后您可以数数。

var posts = await _unitOfWork.Posts
                         .GetAllAsync(p => p.UserId == userId && 
                                           p.IsActive == true, 
                                      l => l.Likes).ToListAsync(); 
var likesCount = posts.Likes.Count();

Answer 2

如果您是 EF Core 的新手，请不要创建通用存储库，这是无用的模式，只会增加复杂性。

正确且最快的查询是：

var likesCount = await _context.Posts
   .Where(p => p.UserId == userId && p.IsActive == true)
   .SelectMany(p => p.Likes)
   .CountAsync();

ef Core Table 关系包含计数错误

Ef Core Table relationship include count Error

c#

ef-code-first

entity-framework-core