在存储库中使用Include()方法

Question

我在EF 5中有以下内容:

var a = context.Posts.Include(x => x.Pack).Select(x => x.Pack.Id).ToList();

这有效.然后我尝试在我的通用存储库中复制它:

public IQueryable<T> Include<T>(Expression<Func<T, Boolean>> criteria) where T : class
{
    return _context.Set<T>().Include(criteria);
}

但在这种情况下,我无法执行以下操作:

var b = repository.Include<Post>(x => x.Pack).Select(x => x.Pack.Id).ToList();

我收到错误:

无法将类型'Data.Entities.Pack'隐式转换为'bool'

我怎么解决这个问题？

我应该在Include()方法中更改什么？

Answer 1

尝试:

更改

Expression<Func<T, Boolean>> criteria

至

Expression<Func<T, object>> criteria

编辑:要包含多个实体,您需要添加"包含"扩展名:

public static class IncludeExtension
{
    public static IQueryable<TEntity> Include<TEntity>(this IDbSet<TEntity> dbSet,
                                            params Expression<Func<TEntity, object>>[] includes)
                                            where TEntity : class
    {
        IQueryable<TEntity> query = null;
        foreach (var include in includes)
        {
            query = dbSet.Include(include);
        }

        return query == null ? dbSet : query;
    }
}

然后你可以像这样使用它:

repository.Include(x => x.Pack, x => x.Pack.Roles, ...).Select(x => x.Pack.Id).ToList();

只需确保"repository"返回"DbSet"对象.

Answer 2

我使用了已接受的答案，但必须针对 EntityFramework Core 对其进行一些修改。根据我的经验，我必须保持链继续运行，否则之前的查询引用将被覆盖。

    public IQueryable<TEntity> Include(params Expression<Func<TEntity, object>>[] includes)
    {
        IIncludableQueryable<TEntity, object> query = null;

        if(includes.Length > 0)
        {
            query = _dbSet.Include(includes[0]);
        }
        for (int queryIndex = 1; queryIndex < includes.Length; ++queryIndex)
        {
            query = query.Include(includes[queryIndex]);
        }

        return query == null ? _dbSet : (IQueryable<TEntity>)query;
    }