Translation of the ‘String.Equals‘ overload with a ‘StringComparison‘ parameter is not supported

朴灿烈づ我的快乐病毒、 2023-01-22 06:53 10阅读 0赞

#### \#事故现场 ####

*  使用.net core ef 连接mysql，进行查询操作，报错如下：

> The LINQ expression ‘DbSet<Ps\_Path>()  
> .Where(p => p.Mark.Equals(  
> value: \_\_Substring\_0,  
> comparisonType: OrdinalIgnoreCase))’ could not be translated. Additional information: Translation of the ‘String.Equals’ overload with a ‘StringComparison’ parameter is not supported by default. To opt-in to translations of methods with a ‘StringComparison’ parameter, call `EnableStringComparisonTranslations` on your MySQL specific ‘DbContext’ options. For general EF Core information about this error, see https://go.microsoft.com/fwlink/?linkid=2129535 for more information. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to ‘AsEnumerable’, ‘AsAsyncEnumerable’, ‘ToList’, or ‘ToListAsync’. See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.

*  开发环境：  
    .net core : .NET 5  
    mysql : 8.0.25  
    mysqlclient包：Pomelo.EntityFrameworkCore.MySql，版本： 5.0

#### \#原因 ####

报错代码：

var path = db.Ps_Path.FirstOrDefault(s =>
                        s.Mark.Equals(fileInfo.RelativePath.Substring(0, 3), StringComparison.OrdinalIgnoreCase));

上面代码使用了比较字符串的StringComparison.OrdinalIgnoreCase参数，`Pomelo.EntityFrameworkCore.MySql`默认不支持，需要配置DbContext；

#### \#解决方法 ####

配置DbContext的`EnableStringComparisonTranslations`属性；

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
     { 
     	var serverVersion = new MySqlServerVersion(new Version(8, 0, 25));
    	optionsBuilder.UseMySql(_configuration.GetConnectionString("mysql"), serverVersion, mySqlOptions => mySqlOptions.EnableStringComparisonTranslations(true));
     }

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