Question

我有2个实体，国家和城市。一个国家可以有许多城市。我想实现以下目标：

IQueryable<Country> query =
    myContext.Countries
             .Select(co => new Country
                 {
                     Id = co.Id,
                     Name = co.Name,
                     Cities = co.Cities.Select(c => new City { Id = c.Id, Name = c.Name })
                 })
             .AsQueryable();

但是函数接受一个属性名称数组，如

string[] columns = new string[] { "Id", "Name", "Cities.Name" }

到目前为止，我尝试修改此平台上看到的以下功能，但它在＆＃34; Cities.Name＆＃34;上引发了异常。不属于国家实体。

public static IQueryable<TResult> Select<TResult>(this IQueryable source, string[] columns)
{
    var sourceType = source.ElementType;
    var resultType = typeof(TResult);
    var parameter = Expression.Parameter(sourceType, "e");
    var bindings = columns.Select(column => Expression.Bind(resultType.GetProperty(column), Expression.PropertyOrField(parameter, column)));
    var body = Expression.MemberInit(Expression.New(resultType), bindings);
    var selector = Expression.Lambda(body, parameter);
    return source.Provider.CreateQuery<TResult>(
        Expression.Call(typeof(Queryable), "Select", new Type[] { sourceType, resultType },
            source.Expression, Expression.Quote(selector)));
}

呼叫：

IQueryable<Country> query = _hotelContext.Countries.Select<Country>(new string[] { "Id", "Name", "Cities.Name" });

return await query.ToListAsync();

请帮助，非常渴望得到答案。干杯

如何从列名列表中动态创建IQueryable <t>

0 个答案: