Question

我正在尝试使用link动态创建where子句。现在，创建像SELECT Product WHERE x = 123 AND y = 349 AND w = 948这样的东西没问题。我只是添加额外的Where过滤器。 products = products.Where(product => product.Property == 123);

但是现在我有一个未知数量的值，应该使用OR运算符进行测试。 SQL应该像SELECT Product WHERE x = 123 OR x = 499 OR x = 998 .. and n more OR's

Answer 1

构建要检查的数字列表，并执行以下操作：

var idsToCheck = new List<int>{123, 789, 654}; //Build from dynamic list
products = products.Where(x => idsToCheck.Contains(x.Id));

如果需要，上面的内容可以复制为v和w

var idsToCheck = new List<int>{123, 789, 654}; //Build from dynamic list
products = products.Where(x => idsToCheck.Contains(x.Id));

var propertyToCheck = new List<int>{123, 789, 654};//Build from dynamic list
products = products.Where(x => propertyToCheck.Contains(x.Property));

var numberToCheck = new List<int>{123, 789, 654};
products = products.Where(x => numberToCheck.Contains(x.Number));

如果要检查的值已经作为枚举传入，那么您不需要构建xxxToCheck集合。您只需针对原件执行.Contains

即可

Answer 2

您可以在列表中使用contains，或者只使用如下公式：

  products.Where(product => (product.Property == 123) || (product.Property == 499) || (product.Property == 998));

Answer 3

如果要从多个where子句组成OR查询，则确实需要在where子句中组合谓词。毕竟，链接的条款将是AND。

所以，如果您有以下谓词：

Func<Product, bool> w1 = p => p.x == 123;
Func<Product, bool> w2 = p => p.y == 349;
Func<Product, bool> w3 = p => p.w == 948;
Func<Product, bool> w4 = p => p.Property == 123;
Func<Product, bool> w5 = p => p.x == 499;
Func<Product, bool> w6 = p => p.x == 998;

您可以将以下扩展方法定义为OR：

public static Func<T, bool> Or<T>(this Func<T, bool> @this, Func<T, bool> that)
{
    return t => @this(t) || that(t);
}

现在你可以写：

var products1 = products.Where(w1.Or(w5).Or(w6));

var products2 = products.Where(
    ((Func<Product, bool>)(p => p.x == 123))
        .Or(p => p.y == 349)
        .Or(p => p.Property == 123));

如果您想使用子句列表，请添加此扩展方法：

public static Func<T, bool> Or<T>(this IEnumerable<Func<T, bool>> @this)
{
    return @this.Aggregate((Func<T, bool>)(t => true), (a, t) => a.Or(t));
}

现在你可以写：

var predicates = new List<Func<Product, bool>>()
{
    p => p.x == 123,
    p => p.w == 948,
    p => p.Property == 123,
    p => p.x == 998,
};

var products3 = products.Where(predicates.Or());

如果您是针对IQueryable<T>提供商撰写的，那么您需要使用Expression<Func<Product, bool>>而不仅仅是Func<Product, bool>。

然后你需要这些扩展方法：

public static Expression<Func<T, bool>> Or<T>(
    this Expression<Func<T, bool>> @this,
    Expression<Func<T, bool>> that)
{
    var param =
        Expression
            .Parameter(typeof(T), "t");
    var body =
        Expression
            .Or(
                Expression
                    .Invoke(@this, param),
                Expression
                    .Invoke(that, param));
    return
        Expression
            .Lambda<Func<T, bool>>(body, param);
}

public static Expression<Func<T, bool>> Or<T>(
    this IEnumerable<Expression<Func<T, bool>>> @this)
{
    return @this.Aggregate((Expression<Func<T, bool>>)(t => true), (a, t) => a.Or(t));
}

调用代码仍然有效：

var predicatesX = new List<Expression<Func<Product, bool>>>()
{
    p => p.x == 123,
    p => p.w == 948,
    p => p.Property == 123,
    p => p.x == 998,
};

var products3X = products.Where(predicatesX.Or());

这是你在找什么？

如何在LINQ中建立动态OR查询？

3 个答案: