我正在使用这里提到的模式
http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-the-repository-and-unit-of-work-patterns-in-an-asp-net-mvc-application
http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-the-repository-and-unit-of-work-patterns-in-an-asp-net-mvc-application
public virtual IEnumerable<TEntity> Get(
Expression<Func<TEntity,bool>> filter = null,Func<IQueryable<TEntity>,IOrderedQueryable<TEntity>> orderBy = null,string includeProperties = "")
{
IQueryable<TEntity> query = dbSet;
if (filter != null)
{
query = query.Where(filter);
}
foreach (var includeProperty in includeProperties.Split
(new char[] { ',' },StringSplitOptions.RemoveEmptyEntries))
{
query = query.Include(includeProperty);
}
if (orderBy != null)
{
return orderBy(query).ToList();
}
else
{
return query.ToList();
}
}
现在我想创建动态Func< IQueryable< TEntity>,IOrderedQueryable< TEntity>>表达式来订购我的数据.
我只知道字段名称为字符串和顺序类型(升序,降序)为字符串(asc,desc)
解决方法
最后我可以写出我想要的方法.
public static Func<IQueryable<TEntity>,IOrderedQueryable<TEntity>> GetOrderBy(string orderColumn,string orderType) {
Type typeQueryable = typeof(IQueryable<TEntity>);
ParameterExpression argQueryable = Expression.Parameter(typeQueryable,"p");
var outerExpression = Expression.Lambda(argQueryable,argQueryable);
string[] props = orderColumn.Split('.');
IQueryable<TEntity> query = new List<TEntity>().AsQueryable<TEntity>();
Type type = typeof(TEntity);
ParameterExpression arg = Expression.Parameter(type,"x");
Expression expr = arg;
foreach(string prop in props) {
PropertyInfo pi = type.GetProperty(prop,BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance);
expr = Expression.Property(expr,pi);
type = pi.PropertyType;
}
LambdaExpression lambda = Expression.Lambda(expr,arg);
string methodName = orderType == "asc" ? "OrderBy" : "OrderByDescending";
MethodCallExpression resultExp =
Expression.Call(typeof(Queryable),methodName,new Type[] { typeof(TEntity),type },outerExpression.Body,Expression.Quote(lambda));
var finalLambda = Expression.Lambda(resultExp,argQueryable);
return (Func<IQueryable<TEntity>,IOrderedQueryable<TEntity>>)finalLambda.Compile();
}
此方法有两个参数,第一个是字段名,另一个是asc或desc.
方法的结果可以直接与IQueryable对象一起使用.
谢谢你的帮助
