在列表< T>中排序外键为null时使用Lambda Expression [英] Order By in List<T> with Lambda Expression when foreign key is null

问题描述

以下是我的查询:

List<db_table> listData = db.db_table.Take(50).ToList();

现在，我希望将此列表作为排序列表.为此，我尝试了:

Now I want this list as sorted list. For that I tried:

listData = db.db_table.OrderBy(x => x.db_table1.column_name).ToList();

那时我的列也包含'null'.

My column contains 'null' also at that time it throws an error.

考虑db_table具有从db_table1分配的外键

Consider that db_table has foreign key assigned from db_table1

推荐答案

您可以扩展lambda表达式或使用

You can extend your lambda expression or using c# 6 features:

// use c# 6.0 ?. operator
listData = db.db_table
             .OrderBy(x => x.db_table1?.column_name)
             .ToList();

// check value manually
listData = db.db_table
             .OrderBy(x => x.db_table1 != null ? x.db_table1.column_name : string.Empty)
             .ToList();

// filter null values before sorting
listData = db.db_table
             .Where(x => x.db_table1 != null)
             .OrderBy(x => x.db_table1.column_name)
             .ToList();

这篇关于在列表< T>中排序外键为null时使用Lambda Expression的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！