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
原文地址:https://www.jb51.cc/csharp/97778.html
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