在 Translate 方法中获取 SqlParameterExpression 值

Question

我正在尝试在 EF Core 5 中实现自定义 IMethodCallTranslator

译者：

public class NpgsqlCustomILikeMethodTranslator : IMethodCallTranslator
{
    private readonly MethodInfo _customILikeMethod = typeof(NpgsqlDbFunctionsExtensions)
       .GetRuntimeMethod(nameof(NpgsqlDbFunctionsExtensions.CustomILike),
                         new[] { typeof(DbFunctions), typeof(string), typeof(string) });

    public SqlExpression Translate(SqlExpression instance,
                                   MethodInfo method,
                                   IReadOnlyList<SqlExpression> arguments,
                                   IDiagnosticsLogger<DbLoggerCategory.Query> logger)
    {
        if (method == _customILikeMethod)
        {
            var pattern = arguments[2];
            if (pattern is SqlParameterExpression patternParameter)
            {
                // Get the value from patternParameter as string
                var patternString = ???;
                
                // Do something with patternString
                patternString = DoWork(patternString);

                // Put changed string as constant
                pattern = new SqlConstantExpression(Expression.Constant(patternString), null); 
            }
            return new PostgresILikeExpression(arguments[1], pattern, null, null);
        }
        return null;
    }
}

用法：

var pattern = "%A%";
query = query.Where(u => EF.Functions.CustomILike(u.Name, pattern);

有什么方法可以从 Translate 方法中获取我的模式字符串值“%A%”？

Answer 1

无法在 IMethodCallTranslator 实现中获取 SqlParameterExpression 的值。所以尝试强制 EF Core 为这种方法生成 SqlConstantExpression。可以通过将 [NotParameterized] 属性添加到所需的函数参数来完成。

public static bool CustomILike(string str, [NotParameterized] string pattern)

在 Translate 方法中获取 SqlParameterExpression 值

Get SqlParameterExpression value inside Translate method

c#

entity-framework-core

ef-core-5.0