EF 4.1/Linq-to-SQL:什么更好:使用 Equals 还是 ==?

作者: 不许调戏小黄鸡
来源: 51数据库
2022-12-13

问题描述

We're having a discussion about using Equals or == on an int comparison in a LINQ query. We're using EF4.1 Code First. What is better?

var query = context.Boodschappen
                   .Where(b => b.BoodschapID == id).FirstOrDefault();

or:

var query = context.Boodschappen
                   .Where(b => b.BoodschapID.Equals(id)).FirstOrDefault();

And why?

解决方案

For Linq To Sql, you want neither. Instead, use Object.Equals: .Where(b => Object.Equals(b.BoodschapID, id)

Why? Because of a Bug in the SQL Generator if id happens to be a nullable uniqueidentifier. If using b.BoodschapID.Equals(id) or b.BoodschapID == id and b.BoodschapID happens to be a nullable Guid, the generated SQL will not be WHERE BoodschapID IS NULL but rather WHERE BoodschapID = @p0 which will not return any results.

I know for sure that EF used to have the same bug. No idea if it's solved yet. You can find more details in this question, just be aware that some of the answers generate horrendous SQL.

Apart from that, there is no difference between Equals and == in Linq To SQL that I'm aware of.

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