EF Core 3 使用扩展方法过滤数据

Question

I am trying to make extension method for querying ef core. I have this Extension:

 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;
     }
  }

and then I am trying to filtr data, but the extension method doing nothing:

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

Can anybody help please?

Answer 1

You should put the result of query.Where(x => x.OrderType == filter.OrderType);into query like this

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

You have to return the results:

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;
     }
  }

You can user regular expressions:

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