LINQ to object 和通用 PredicateBuilder 似乎不能很好地协同工作

Question

我有一个场景可以使用下面的代码来简化这里的解释。

我有模型class

class Model
{
    public string CodeLevel1 { get; set; }
    public string CodeLevel2 { get; set; }
    public bool IsVoluntary { get; set; }
}

很明显我会建立一个对象列表

        var models = new List<Model>
        {
            new Model()
            {
                CodeLevel1 = "32",
                CodeLevel2 = "A1",
                IsVoluntary = false
            },
            new Model()
            {
                CodeLevel1 = "32",
                CodeLevel2 = "A2",
                IsVoluntary = true
            },
            new Model()
            {
                CodeLevel1 = "33",
                CodeLevel2 = "A3",
                IsVoluntary = true
            },
            new Model()
            {
                CodeLevel1 = "34",
                CodeLevel2 = "A4",
                IsVoluntary = false
            },
            new Model()
            {
                CodeLevel1 = "34",
                CodeLevel2 = "A5",
                IsVoluntary = false
            },
            new Model()
            {
                CodeLevel1 = "34",
                CodeLevel2 = "A6",
                IsVoluntary = true
            },
        };

我想使用 A universal PredicateBuilder 中介绍的 PredicateBuilder 来构建动态查询。以下代码只是我尝试的第一步。

var configs = new Dictionary<string, List<string>>()
{
    { "32", new List<string>() { "A1", "A2"} },
    { "33", new List<string>() { "A3" } },
};
var predicate = PredicateBuilder.False<Model>();
var allLevel1CodesInConfig = (from c in configs select c.Key).ToList();
predicate.Or(x => !allLevel1CodesInConfig.Contains(x.CodeLevel1) && x.IsVoluntary == false);
var filteredList = models.AsQueryable().Where(predicate).ToList();

我在 filteredList 中什么也没得到，但如果我重写最后一行代码，我就会得到我所期望的。

var filteredList = models.AsQueryable().Where(x => !allLevel1CodesInConfig.Contains(x.CodeLevel1) && x.IsVoluntary == false).ToList();

我需要一些帮助来理解为什么 Where 中的谓词对我不起作用？

Answer 1

问题出在这一行：

predicate.Or(x => !allLevel1CodesInConfig.Contains(x.CodeLevel1) && x.IsVoluntary == false);

改为：

predicate = predicate.Or(x => !allLevel1CodesInConfig.Contains(x.CodeLevel1) && x.IsVoluntary == false);

每个 PredicateBuilder 方法都会创建一个新谓词并且不会改变原始谓词。

LINQ to object 和通用 PredicateBuilder 似乎不能很好地协同工作

LINQ to object and universal PredicateBuilder does not seem to play well together

c#

linq

lambda

expression-trees