LINQ查询与数组输入和变量Where声明 - 建议

Question

我想查询给定数组的数据,以使用Silverlight客户端API通过WCF数据服务进行筛选.基本上,我想查询给定列表(数组)状态的Employees.

我在想这样的事情:

public IQueryable<Employee> Load(string[] states)
{
     foreach (var x in states)
     {
           // LINQ query here with 1 to N .Where statements
           return from e in Context.Employees
           .Where(...)
     }
} 

所以,假设我的数组中有2个项目,即我想通过2个状态进行查询,我会手动执行以下操作:

return from e in Context.Employees
    .Where(e => e.State== states[0] || e.State == states[1])));

任何建议将不胜感激!

Answer 1

您可以为条件动态构建表达式树.

var parameter = Expression.Parameter(typeof(Employee), "employee");

Expression condition = Expression.Constant(false);

foreach (var state in states)
{
    condition = Expression.OrElse(
        condition,
        Expression.Equal(
            Expression.Property(parameter, "State"),
            Expression.Constant(state)));
}

var expression = Expression.Lambda<Func<Employee, Boolean>>(condition, parameter);

然后只是执行调用.

var result = Context.Employees.Where(expression);

我不是100%肯定这是否会制定出适合您的箱子,但我希望的总体思路帮助.