.Net Core 3.1 Web Api 中的规范模式

如何解决.Net Core 3.1 Web Api 中的规范模式

我对搜索方法使用规范查询，它包括搜索、orderBy、groupBy。 Search 和 Orderby 没问题，但我在这一行的 groupBy 方法中遇到问题 query.GroupBy(spec.GroupBy).SelectMany(x => x)

请查看以下代码：

 public async Task<PaginatedResult<List<EmployeeTypeResponse>>> Handle(GetAllEmployeeTypesQuery request,CancellationToken cancellationToken)
        {

            var employeeTypesWithPaging = _employeeTypeRepository.FindWithSpecificationPattern(new Employeetypespecifcation(request.Filter,true),true);

我想在 ApplyGroupBy(x => x.ShopId); 处使用 ShopId 申请 groupBy；

   public class Employeetypespecifcation : BaseSpecifcation<EmployeeType>
   {
    public Employeetypespecifcation()
    {

    }
    public Employeetypespecifcation(PaginationFilter Filter,bool isPaging)
    {

        if (!string.IsNullOrEmpty(Filter.GroupBy))
        {
            ApplyGroupBy(x => x.ShopId);
        }

        var predicate = PredicateBuilder.True<EmployeeType>();

        if (!string.IsNullOrEmpty(Filter.SearchText))
        {
            predicate = predicate.And(x => x.Name.Contains(Filter.SearchText) || x.Code.Contains(Filter.SearchText));
        }

        if (Filter.ShopId != null)
        {
            predicate = predicate.And(c => c.ShopId == Filter.ShopId);
        }

    }
}

像这样的 BaseSpecifcation 类

 public class BaseSpecifcation<T> : ISpecification<T>
{
    public BaseSpecifcation()
    {
    }
    public BaseSpecifcation(Expression<Func<T,bool>> criteria)
    {
        Criteria = criteria;
    }

    public Expression<Func<T,object>> OrderBy { get; private set; }
    public Expression<Func<T,object>> OrderByDescending { get; private set; }
    public Expression<Func<T,object>> GroupBy { get; private set; }

    protected virtual void ApplyGroupBy(Expression<Func<T,object>> groupByExpression)
    {
        GroupBy = groupByExpression;
    }
    protected void AddOrderBy(Expression<Func<T,object>> orderByExpression)
    {
        OrderBy = orderByExpression;
    }
    protected void AddOrderByDescending(Expression<Func<T,object>> orderByDescExpression)
    {
        OrderByDescending = orderByDescExpression;
    }
    
}

FindWithSpecificationPattern 和 GetQuery 方法：

 public IEnumerable<T> FindWithSpecificationPattern(ISpecification<T> specification = null,bool isPaging = false)
    {         
        return  SpecificationEvaluator<T>.GetQuery(DbContext.Set<T>().AsQueryable(),specification,isPaging);
    }

   public class SpecificationEvaluator<TEntity> where TEntity : class
{
    public static IQueryable<TEntity> GetQuery(IQueryable<TEntity> inputQuery,ISpecification<TEntity> spec,bool isPaging)
    {
        var query = inputQuery;

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

        if (spec.GroupBy != null)
        {
            query = query.GroupBy(spec.GroupBy).SelectMany(x => x);
        }
    }
}

我在这条线上遇到了问题

query = query.GroupBy(spec.GroupBy).SelectMany(x => x);

虽然它不会抛出异常，但我无法得到结果。当我调试时，我看到错误消息

Query='((Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable)query).DebugView.Query' 引发了类型为“system.invalidOperationException”的异常>

我在 Google 中搜索了很多次，但没有看到任何使用规范模式实现 GroupBy 的示例。 请帮帮我，非常感谢！