实体框架EF.Functions.Like与字符串。包含

问题描述

我正在阅读实体框架核心2.0的公告

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/

它说他们添加了新的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。包含 / 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

两个版本之间有什么区别？
EF已经知道如何将 string.Contains / StartsWith 转换为相应的SQL操作，但是

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会允许使用更复杂的模式，例如 a％b％ （尽管可以将其写为 StartsWith（ a）&& Contains（ 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"))

这是原因吗？

推荐答案

像查询一样支持，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_");

或从以元音开头的城市中吸引所有客户：

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的答案，了解它们如何不同地转换为SQL查询）

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

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