实体框架 EF.Functions.Like 与 string.Contains [英] Entity framework EF.Functions.Like vs string.Contains

问题描述

我正在阅读实体框架核心 2.0 的公告 https://blogs.msdn.microsoft.com/dotnet/2017/08/14/announcing-entity-framework-core-2-0/

I was reading the announcement of entity framework core 2.0 https://blogs.msdn.microsoft.com/dotnet/2017/08/14/announcing-entity-framework-core-2-0/

据说他们添加了新的 Sql 函数，例如 EF.Functions.Like 来执行 SQL LIKE 操作.

It says that they added new Sql functions like EF.Functions.Like for performing the SQL LIKE operation.

我想知道，EF.Functions.Like 和 string.Contains/StartsWith 之间有什么区别?

I was wondering, what then would be the difference between EF.Functions.Like and string.Contains/StartsWith?

例如:

var customers = context.Customers.Where(c => c.Name.StartsWith("a")); // Version A
var customers = context.Customers.Where(c => EF.Functions.Like(c.Name, "a%")); // Version B

这两个版本有什么区别?EF 已经知道如何将 string.Contains/StartsWith 翻译成相应的 SQL 操作，不是吗?

What would be the difference between the two versions? EF already knows how to translate string.Contains/StartsWith to the corresponding SQL operations, doesn't it?

我能想到的唯一原因是 EF.Functions.Like 将允许更复杂的模式，如 "a%b%"(虽然这个可以写成 StartsWith("a") &&包含("b"))

The only reason i can think of is that EF.Functions.Like would allow for more complex patterns like "a%b%" (although this one can be written as StartsWith("a") && Contains("b"))

是这个原因吗?

推荐答案

Like 查询支持通配符 因此在某些情况下与字符串扩展方法相比非常有用.

Like query supports wildcard characters and hence very useful compared to the string extension methods in some scenarios.

例如:如果我们要搜索所有以 'ri' 作为中间字符的 4 个字母名称，我们可以执行 EF.Functions.Like(c.Name, "_ri_");

For ex: If we were to search all the 4 lettered names with 'ri' as the middle characters we could do EF.Functions.Like(c.Name, "_ri_");

或者从以元音开头的城市获取所有客户:

or to get all the customers from cities which start with vowels:

var customers = from c in context.Customers 
                   where EF.Functions.Like(c.City, "[aeiou]%")
                   select c;

(请阅读@Tseng 的回答，了解它们如何以不同的方式转换为 SQL 查询)

(Please read @Tseng's answer on how they are translated differently into SQL queries)

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