如何拼接Expression查询条件

在执EF多条件查询的时候，如果查询字段比较多、查询比较复杂需要动态的构建Expression条件，怎样将这些条件拼接在一起？

在论坛中查了一些关于《动态Lambda表达式》的例子，都比较复杂，有没有什么简便的方法？

望高手赐教！

比如下面的三个查询条件：

Expression<Func<Model.PM_PickStore, bool>> predicate1 = null;

if (PlanNo == "") { predicate1= o => o.DevID == 1; }

Expression<Func<Model.PM_PickStore, bool>> predicate2 = null;

if (PlanNo == "") { predicate2 = o => o.DevID == 2; }

Expression<Func<Model.PM_PickStore, bool>> predicate3 = null;

if (PlanNo == "") { predicate3 = o => o.DevID == 3; }

 

var expression = Expression.Equal(Expression.Constant(1), Expression.Constant(1));
var parameterExpression = Expression.Parameter(typeof(Model.PM_PickStore), "p");
var propertyExpression = Expression.Property(parameterExpression, "DevID");
if (PlanNo == "") { expression = Expression.AndAlso(expression, Expression.Equal(propertyExpression, Expression.Constant(1)));}
if (PlanNo == "") { expression = Expression.AndAlso(expression, Expression.Equal(propertyExpression, Expression.Constant(2))); }
if (PlanNo == "") { expression = Expression.AndAlso(expression, Expression.Equal(propertyExpression, Expression.Constant(3))); }

 

我在网上找了一个封装的方法，通过下面的代码可以实现了

　　　　var list = new List<Expression<Func<Model.PM_PickStore, bool>>>();
            list.Add(o => true);
            if (DevID != 0) list.Add(o => o.DevID == DevID);
            if (StoreID != 0) list.Add(o => o.StoreID == StoreID);
            if (PlanNo != "") list.Add(o => o.PlanNo.Equals(PlanNo));
            Expression<Func<Model.PM_PickStore, bool>> productQueryTotal = null;
            foreach (var expression in list)
            {
                productQueryTotal = expression.And(expression);
            }