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应用程序
我正在使用下面的方法来查询 EF
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>>
表达式来排序我的数据。
我只知道字段名称为字符串,顺序类型(升序、降序)为字符串(asc、desc)
终于可以写出我想要的方法了。
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();
}
该方法有两个参数,第一个是字段名称,另一个是 asc 或 desc。
方法的结果可以直接与 IQueryable 对象一起使用。
感谢您的帮助
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