Question

我正在尝试开发用于查询ef核心的扩展方法。我有这个扩展程序：

 public static class FiltrExtension
  {
     public static IQueryable<Contract> Filtr(this IQueryable<Contract> query, OrderFilter filter) 
     {
      if (!string.IsNullOrWhiteSpace(filter.OrderType))
         query.Where(x => x.OrderType == filter.OrderType);
      return query;
     }
  }

然后我尝试过滤数据，但是扩展方法什么也不做：

var data = await _uow.DatabaseContext.Contract.Filtr(filter).ToListAsync();

有人可以帮忙吗？

Answer 1

您应像这样将query.Where(x => x.OrderType == filter.OrderType);的结果放入query

public static class FiltrExtension
  {
     public static IQueryable<Contract> Filtr(this IQueryable<Contract> query, OrderFilter filter) 
     {
      if (!string.IsNullOrWhiteSpace(filter.OrderType))
        query = query.Where(x => x.OrderType == filter.OrderType);
      return query;
     }
  }

Answer 2

您必须返回结果：

public static class FiltrExtension
  {
     public static IQueryable<Contract> Filtr(this IQueryable<Contract> query, OrderFilter filter) 
     {
      if (!string.IsNullOrWhiteSpace(filter.OrderType))
         var result = query.Where(x => x.OrderType == filter.OrderType);
      return result;
     }
  }

您可以使用正则表达式：

  public static IQueryable<Contract> And<Contract>(this IQueryable<Contract> source, Expression<Func<Contract, bool>> predicate)
    {   
      return source.Where(predicate);    
    }

EF Core 3使用扩展方法过滤数据

2 个答案: