表达式树 InvalidOperationException：无法解析 LINQ 表达式

Question

我目前正在尝试转换这个：

users.Where(s => EF.Functions.Like(EF.Functions.Collate(s.Username, "Latin1_General_CI_AI"), $"%{searchString}%"));

进入表达式树函数（下面的代码）。我用这个 answer

走到了这一步

public static IQueryable<T> IgnoreAccentSearch<T>(this IQueryable<T> queryable, string searchString, string property)
{
    // Get our generic object
    ParameterExpression entity = Expression.Parameter(typeof(T), "entity");

    // get the Collate method from EF.Functions
    var efCollatMethod = typeof(RelationalDbFunctionsExtensions)
        .GetMethod("Collate")
        .MakeGenericMethod(typeof(T));

    // Get the Like Method from EF.Functions
    var efLikeMethod = typeof(DbFunctionsExtensions).GetMethod("Like",
        BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic,
        null,
        new[] { typeof(DbFunctions), typeof(string), typeof(string) },
        null);

    // We make a pattern for the search
    var pattern = Expression.Constant($"%{searchString}%", typeof(string));

    // make the collate constant
    var collate = Expression.Constant("Latin1_General_CI_AI", typeof(string));

    // Create the collate expression
    Expression collateExpression = Expression.Call(efCollatMethod,
        Expression.Property(null, typeof(EF), nameof(EF.Functions)), entity, collate);

    // Get property from our object
    var propertyExpression = Expression.Property(collateExpression, property);

    // Сall the method with all the required arguments
    Expression whereExpression = Expression.Call(efLikeMethod,
         Expression.Property(null, typeof(EF), nameof(EF.Functions)), propertyExpression, pattern);

    // Compose and pass the expression to Where
    var expression = Expression.Lambda<Func<T, bool>>(whereExpression, entity);
    return queryable.Where(expression);
}

我收到以下错误消息：

InvalidOperationException: The LINQ expression 'DbSet() .Where(u => __Functions_0 .Like( matchExpression: __Functions_0 .Collate( operand: u, collation: "Latin1_General_CI_AI").Username, pattern: "%K%"))' could not be translated. 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.

所以我做错了什么。有人能帮我一下吗？我以前没有用过很多表达式树，所以欢迎任何信息。

Answer 1

通常，如果可能的话，我试图强制编译器完成大部分工作：

public static IQueryable<T> IgnoreAccentSearch<T>(this IQueryable<T> queryable, string searchString, string property)
{
    // defining Expression Template with two input parameters
    Expression<Func<string, string, bool>> predicateTemplate = 
        (prop, value) => EF.Functions.Like(EF.Functions.Collate(prop, "Latin1_General_CI_AI"), $"%{value}%"));

    var entityParam = Expression.Parameter(typeof(T), "entity");
    var propExpr = Expression.PropertyOrField(entityParam, property);
    var searchExpr = Expression.Constant(searchString);

    var body = predicateTemplate.Body;
    
    // injecting needed values instead of parameters
    body = ReplacingExpressionVisitor.Replace(predicateTemplate.Parameters[0], propExpr, body);
    body = ReplacingExpressionVisitor.Replace(predicateTemplate.Parameters[1], searchExpr, body);

    var lambda = Expression.Lambda<Func<T, bool>>(body, entityParam);

    return queryable.Where(lambda);
}

表达式树 InvalidOperationException：无法解析 LINQ 表达式

Expression tree InvalidOperationException: The LINQ expression can't be resolved

c#

entity-framework-core

.net-core