//构造Lambda语句
       private static Expression<Func<TElement, bool>> BuildWhereInExpression<TElement, TValue>(Expression<Func<TElement, TValue>> propertySelector, IEnumerable<TValue> values)
        {
            ParameterExpression p = propertySelector.Parameters.Single();
            if (!values.Any())
                return e => false;

            var equals = values.Select(value => (Expression)Expression.Equal(propertySelector.Body, Expression.Constant(value, typeof(TValue))));
            var body = equals.Aggregate<Expression>((accumulate, equal) => Expression.Or(accumulate, equal));

            return Expression.Lambda<Func<TElement, bool>>(body, p);
        }

//调用
      string[] ids = new string[]{"id1","id2","id3"}；
      db.ProjectFiles.Where(BuildWhereInExpression<Profile,int>(v=>v.Id,ids);

//封装方法

        public static IQueryable<TElement> WhereIn<TElement, TValue>(this IQueryable<TElement> source, Expression<Func<TElement, TValue>> propertySelector, params TValue[] values)
        {
            return source.Where(BuildWhereInExpression(propertySelector, values));
        }
//直接使用下列方法调用

      string[] ids = new string[]{"id1","id2","id3"}；
      db.ProjectFiles.WhereIn(c => c.Id,ids);
//字符串构造
//这个方法比较简单

      string[] ids = new string[]{"id1","id2","id3"}；
      cstIds=cstIds.Replace(",","','");
      var query = db.ProjectFiles.Where("it.Id in {'" + cstIds + "'}");