FromSqlInterpolated/FromSqlRaw 中的 LIKE 运算符不起作用，但流畅的 API 或 LINQ 表达式可以

Question

我正在尝试使用 .NET 3.1 上的 EF Core。我有以下代码摘录：

public static async Task<Task> getWithName(HttpContext c) {
            var name = c.Request.RouteValues["name"].ToString();

            // with API - WORKS!
            var authors = await DB.Authors.Where(a => a.first_name.Contains(name)).ToListAsync();
            // with raw SQL interpolated - BROKEN
            var authors2 = await DB.Authors.FromSqlInterpolated($"SELECT * FROM author WHERE first_name like '%{name}%'").ToListAsync();
            // with raw SQL parametrized - BROKEN
            var authors3 = await DB.Authors.FromSqlRaw("SELECT * FROM author WHERE first_name like '%{0}%'", name).ToListAsync();
            // with LINQ expressions - WORKS!
            var authors4 = await (from a in DB.Authors where a.first_name.Contains(name) select a).ToListAsync();

            c.Response.ContentType = "application/json";
            return c.Response.WriteAsync(Serialize(authors));
        }

除了该方法缺少上下文之外，让我感到困惑的是，Fluent API 版本和 LINQ 查询表达式版本都按预期工作，返回数据库中的 12 项。相反，插值 SQL 和原始 SQL 都无法返回 0 项。

请注意：这并不是我遇到异常或任何错误。它们只是返回 0 个结果，就好像查询是错误的一样。

为了进行原始测试，我只是放置了一个断点，复制名称值并直接在 pgAdmin 中执行查询。该查询按预期工作，返回相同的 12 个项目。

这是您在代码中看到的 4 个查询的（相当复杂的）调试输出：

#this is the DB init debug output

info: Microsoft.EntityFrameworkCore.Infrastructure[10403]
      Entity Framework Core 3.1.4 initialized 'AuthorContext' using provider 
'Npgsql.EntityFrameworkCore.PostgreSQL' with options: None

#this is the fluent API query, which works

info: Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (14ms) [Parameters=[@__name_0='?'], CommandType='Text', CommandTimeout='30']
      SELECT a.id, a.first_name, a.last_name, a.nationality
      FROM public.author AS a
      WHERE (@__name_0 = '') OR (STRPOS(a.first_name, @__name_0) > 0)

#this is the raw SQL, which fails

info: Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (7ms) [Parameters=[p0='?'], CommandType='Text', CommandTimeout='30']
      SELECT * FROM author WHERE first_name like '%@p0%'

#this is the interpolated SQL, which fails too

info: Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (5ms) [Parameters=[p0='?'], CommandType='Text', CommandTimeout='30']
      SELECT * FROM author WHERE first_name like '%@p0%'

#this is the LINQ expression query, which works

info: Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (1ms) [Parameters=[@__name_0='?'], CommandType='Text', CommandTimeout='30']
      SELECT a.id, a.first_name, a.last_name, a.nationality
      FROM public.author AS a
      WHERE (@__name_0 = '') OR (STRPOS(a.first_name, @__name_0) > 0)

我看到 LINQ/Fluent 版本以一种我无法理解的相当奇怪的 SQL 进行转换，但不幸的是，我也不明白为什么代码没有在原始/插值 SQL 中正确扩展我的参数。

谢谢您的任何提示！

Answer 1

好的，

我懂了！与此同时，ErikEJ 在评论中做出了回应。

TL; DR：基本上您需要将通配符包含到原始 C# 变量中

在我原来的代码中存在很多问题：

1. 将参数扩展为 like 语句在普通 Postgres 中甚至不起作用。让我解释一下：当我使用 pgAdim 测试原始查询时，我编写了直接查询。假设作者的名字是matteo。我已将查询测试为：

SELECT * FROM author WHERE first_name like '%matteo%'

不管怎样，任何数据库连接层都可能面向准备好的语句而不是原始查询，因此我在 SQL 中尝试了这个新代码：

DEALLOCATE foo;
PREPARE foo (text) AS
    SELECT * FROM author WHERE first_name like '%$1%';

execute foo('matteo');

这在 SQL 中也失败了！

2. 在普通 SQL 中，作为预准备语句的工作原理是：

DEALLOCATE foo;
PREPARE foo (text) AS
    SELECT * FROM author WHERE first_name like $1;

execute foo('%matteo%');

所以我尝试过这段代码：

public static async Task<Task> getWithName(HttpContext c) {
            var name = c.Request.RouteValues["name"].ToString();
            var name2 = "'%"+name+"%'"; //<- please notice the single quote for SQL strings!

            // with API - WORKS!
            var authors = await DB.Authors.Where(a => a.first_name.Contains(name)).ToListAsync();
            // with raw SQL interpolated - BROKEN

            var authors2 = await DB.Authors.FromSqlInterpolated($"SELECT * FROM author WHERE first_name like {name2}").ToListAsync();
            // with raw SQL parametrized - BROKEN
            var authors3 = await DB.Authors.FromSqlRaw("SELECT * FROM author WHERE first_name like {0}", name2).ToListAsync();
            // with LINQ expressions - WORKS!
            var authors4 = await (from a in DB.Authors where a.first_name.Contains(name) select a).ToListAsync();

            c.Response.ContentType = "application/json";
            return c.Response.WriteAsync(Serialize(authors));
        }

不幸的是这又失败了。

3. 我的代码失败的原因如下：EF Core已经从 C# 字符串转换为 SQL 文本类型，因此不需要单引号！我的代码类似于：

DEALLOCATE foo;
PREPARE foo (text) AS
    SELECT * FROM author WHERE first_name like $1;

execute foo(''%matteo%''); //<- double single quote caused by the EF Core automatic cast.

所以问题的解决方案是：

public static async Task<Task> getWithName(HttpContext c) {
            var name = c.Request.RouteValues["name"].ToString();
            var name2 = "%"+name+"%"; //<- please notice: NO MORE single quote!
            // with API - WORKS!
            var authors = await DB.Authors.Where(a => a.first_name.Contains(name)).ToListAsync();
            // with raw SQL interpolated - BROKEN

            var authors2 = await DB.Authors.FromSqlInterpolated($"SELECT * FROM author WHERE first_name like {name2}").ToListAsync();
            // with raw SQL parametrized - BROKEN
            var authors3 = await DB.Authors.FromSqlRaw("SELECT * FROM author WHERE first_name like {0}", name2).ToListAsync();
            // with LINQ expressions - WORKS!
            var authors4 = await (from a in DB.Authors where a.first_name.Contains(name) select a).ToListAsync();

            c.Response.ContentType = "application/json";
            return c.Response.WriteAsync(Serialize(authors));
        }

基本上您需要将通配符包含到原始 C# 变量中

新问题：除了这个丑陋的通配符包含之外，还有其他解决方案吗？！