如何为多列OrderBy表达式创建表达式树 [英] How to create Expression Tree for multiple column OrderBy Expression

问题描述

我为EF通用存储库创建了一个orderby表达式，如下所示字符串命令= orderByDesc?"OrderByDescending":"OrderBy";

I have create an orderby expression for my EF generic Repository as following string command = orderByDesc ? "OrderByDescending" : "OrderBy";

var type = typeof(T);

var property = type.GetProperty(orderby);

var parameter = Expression.Parameter(type, "p");

var propertyAccess = Expression.MakeMemberAccess(parameter, property);

var orderByExpression = Expression.Lambda(propertyAccess, parameter);

var resultExpression = Expression.Call(typeof(Queryable), command, new Type[] { type, property.PropertyType },

                       items.Expression, Expression.Quote(orderByExpression));
items = items.Provider.CreateQuery<T>(resultExpression);

现在，我想创建包含2列的表达式以进行订购，但找不到有用的东西.

Now I want to create the Expression with 2 columns for ordering and wasn't able to find out something helpful.

请帮助我创建一个包含2列的orderby表达式.

Please help me to create an orderby expression with 2 columns.

推荐答案

通过调用 OrderBy()，然后零次或多次调用 ThenBy()<，LINQ中的多列排序可以工作/code>.您无法通过单次调用 OrderBy()来做到这一点.

Ordering by multiple columns in LINQ works by calling OrderBy() followed by zero or more calls to ThenBy(). You can't do this using a single call to OrderBy().

例如，如果您想按 a 和 b 列进行排序，则必须生成一个类似于以下内容的表达式:

For example, if you can want to sort by the columns a and b, you will have to generate an expression that looks something like:

items.OrderBy(p => p.a).ThenBy(p => p.b)

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