c# ef 排序字段动态,构建动态Lambda和扩展方法OrderBy

时间:2022-04-23 16:41:32

1.动态构建排序 Lambda

        /// <summary>
/// 获取排序Lambda(如果动态排序,类型不同会导致转换失败)
/// </summary>
/// <typeparam name="T">数据字段类型</typeparam>
/// <typeparam name="Tkey">排序字段类型</typeparam>
/// <param name="defaultSort">默认的排序字段</param>
/// <param name="sort">当前排序字段</param>
/// <returns></returns>
public static Expression<Func<T, Tkey>> SortLambda<T, Tkey>(string defaultSort, string sort)
{
//1.创建表达式参数(指定参数或变量的类型:p)
var param = Expression.Parameter(typeof(T), "t");
//2.构建表达式体(类型包含指定的属性:p.Name)
var body = Expression.Property(param, string.IsNullOrEmpty(sort) ? defaultSort : sort);
//3.根据参数和表达式体构造一个lambda表达式
return Expression.Lambda<Func<T, Tkey>>(Expression.Convert(body, typeof(Tkey)), param);
}

使用方法:

        public IQueryable<T> GetModelsByPage<Tkey>(int pageSize, int pageIndex, bool isAsc,
Expression<Func<T, Tkey>> orderByLambda, Expression<Func<T, bool>> whereLambda, out int total)
{
total = dbContext.Set<T>().Where(whereLambda).Count(); //是否升序
if (isAsc)
{
return dbContext.Set<T>().Where(whereLambda).OrderBy(orderByLambda).Skip((pageIndex - ) * pageSize).Take(pageSize);
}
else
{
return dbContext.Set<T>().Where(whereLambda).OrderByDescending(orderByLambda).Skip((pageIndex - ) * pageSize).Take(pageSize);
}
}

缺点:Tkey必须限定,但不一定知道字段类型,错误的类型会导致转换失败,切返回值不能固定为object,如有其他方法,希望大牛给出建议。


2.对ef的OrderBy方法进行扩展(此方法无需指定类型)

    /// <summary>
/// 查询扩展方法
/// </summary>
public static class QueryableExtension
{
public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> query, string propertyName)
{
return _OrderBy<T>(query, propertyName, false);
}
public static IOrderedQueryable<T> OrderByDescending<T>(this IQueryable<T> query, string propertyName)
{
return _OrderBy<T>(query, propertyName, true);
} static IOrderedQueryable<T> _OrderBy<T>(IQueryable<T> query, string propertyName, bool isDesc)
{
string methodname = (isDesc) ? "OrderByDescendingInternal" : "OrderByInternal"; var memberProp = typeof(T).GetProperty(propertyName); var method = typeof(QueryableExtension).GetMethod(methodname)
.MakeGenericMethod(typeof(T), memberProp.PropertyType); return (IOrderedQueryable<T>)method.Invoke(null, new object[] { query, memberProp });
}
public static IOrderedQueryable<T> OrderByInternal<T, TProp>(IQueryable<T> query, System.Reflection.PropertyInfo memberProperty)
{//public
return query.OrderBy(_GetLamba<T, TProp>(memberProperty));
}
public static IOrderedQueryable<T> OrderByDescendingInternal<T, TProp>(IQueryable<T> query, System.Reflection.PropertyInfo memberProperty)
{//public
return query.OrderByDescending(_GetLamba<T, TProp>(memberProperty));
}
static Expression<Func<T, TProp>> _GetLamba<T, TProp>(System.Reflection.PropertyInfo memberProperty)
{
if (memberProperty.PropertyType != typeof(TProp)) throw new Exception(); var thisArg = Expression.Parameter(typeof(T));
var lamba = Expression.Lambda<Func<T, TProp>>(Expression.Property(thisArg, memberProperty), thisArg); return lamba;
}
}

使用方法:

        public IQueryable<T> GetModelsByPage(int pageSize, int pageIndex, bool isAsc, string orderByField, Expression<Func<T, bool>> whereLambda, out int total)
{
total = dbContext.Set<T>().Where(whereLambda).Count(); //是否升序
if (isAsc)
{
return dbContext.Set<T>().Where(whereLambda).OrderBy(orderByField).Skip((pageIndex - ) * pageSize).Take(pageSize);
}
else
{
return dbContext.Set<T>().Where(whereLambda).OrderByDescending(orderByField).Skip((pageIndex - ) * pageSize).Take(pageSize);
}
}

缺点:朕看不懂!