使用实体框架时为Select()创建通用选择器 [英] Create generic selector for Select() while using Entity Framework

问题描述

我想创建一个函数来检索给定属性名称的类型的列表.但是我还不知道如何创建一个可运行的lambda选择器.

I would like to create a function to retrieve a List of a given property name's Type. But i dont know yet how to create a working lambda selector.

public IList<object> GetDistinctListOfProperty(string propertyName)
{
    var propInfoByName = typeof(T).GetProperty(propertyName);
    if (propInfoByName == null) return new List<object>();

    using (var db = new ApplicationDbContext())
    {
        var lambda = //TODO
        return db.Set<T>().Select(lambda).Distinct().ToList();
    }
}

推荐答案

您可以使用此方法生成lambda

You can use this method to generate lambda

public static Expression<Func<T, object>> LambdaGenerator<T>(string propertyName)
    {
        var arg = Expression.Parameter(typeof(T), "current");
        var property = Expression.Property(arg, propertyName);
        var conv = Expression.Convert(property, typeof(object));
        var exp = Expression.Lambda<Func<T, object>>(conv, new ParameterExpression[] { arg });
        return exp;
    }

然后使用此方法创建您的表达式

and then use this method to create your expression

var lambda = LambdaGenerator<T>("Your Property Name");

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