predicate | 易学教程

Specification/Predicate to Search Nested Objects

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问题 I'm using Spring Boot with Spring JPA and Specification Executor. I have my Specification/Predicate combo successfully searching the simple attributes within my class. However, I am having difficulties searching the objects within. Do they need a separate Specification? I have a class that has 2 Many To One mapping classes within and would like to search those fields from within the same class. Predicate Implementation public Specification<User> getSpecification(SpecificationField field,

Java - Use predicate without lambda expressions

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问题 I've below requirement:- Employee.java public boolean isAdult(Integer age) { if(age >= 18) { return true; } return false; } Predicate.java private Integer age; Predicate<Integer> isAdult; public PredicateAnotherClass(Integer age, Predicate<Integer> isAdult) { this.age = age; System.out.println("Test result is "+ isAdult(age)); } public void testPredicate() { System.out.println("Calling the method defined in the manager class"); } Now My goal is to test whether the age which i pass to

How to specify nested “not” operation in specific group id in AEM?

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问题 I have a little complex predicator in which I need to have some nested not operation path=/content/course/ type=cq:Page group.1_daterange.lowerBound=2019-06-12T13:39:19.358Z group.1_daterange.property=jcr:content/xyz group.2_daterange.upperBound=2019-06-12T13:39:19.358Z group.2_daterange.property=jcr:content/abc group.3_relativedaterange.property=jcr:content/courseStartDate group.3_relativedaterange.lowerBound=0 group.p.not=true I don’t want to include the result of group 1 and group 2 hence

Zend Framework 2 Db: Make a part of the query negative using Predicate objects

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问题 How do you negate a part of the query using Zend Framework 2? I'm trying to do the Zend\Db equivalent of this dynamic MySQL query-part: NOT (`a` = 1 AND `b`IS NULL AND `c` LIKE 'foo') Right now I have the three query-parts as Predicate objects (Operator, IsNull and Like objects) . How can I negate these and put in the where? Is it possible to convert a Predicate object (like an Operator or IsNull object) to a Sql String? 回答1: Zend dose not have a out of box solution for this , I wrote a class

Swapping a specific number in list 1 with a specific number in list 2

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问题 I have been brushing up on some Prolog recently. I kind of enjoy just coming up with random problems to try and solve and then working them out. This one is quite tough though, and I'm not one to give up on a problem that I have set out to solve. The problem: I want to make a predicate that will have 2 predetermined lists, 2 numbers to swap, and then output the lists after the swapping is done. Further Explanation: I made it a little harder on myself by wanting to find a specific unique

Swapping a specific number in list 1 with a specific number in list 2

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Create predicate with nested classes with Expression

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问题 I have this : public class Company { public int Id { get; set; } public string Name { get; set; } } public class City { public int Id { get; set; } public string Name { get; set; } public int ZipCode { get; set; } } public class Person { public int Id { get; set; } public string FirstName { get; set; } public string LastName { get; set; } public int? Age { get; set; } public City City { get; set; } public Company Company { get; set; } } I'd like a some case generate the predicate like this :

Expression.Call - Calling linq extension: FirstOrDefault, Where

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问题 I am trying to create the following dynamically, however I am having problems calling the extension method FirstOrDefault : using(var context = new Entities()) { var list = context.Engines.Include("Cars").Select(e => e.Cars.FirstOrDefault()).ToList(); } I have the following Expression parameter = Expression.Parameter(typeof(Engine), "e"); Expression property = Expression.Property(parameter, "Cars"); parameter = {e} property = {e.Cars} Those are good, but I am encountering a problem when I try

What is a pure function?

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问题 I found this quote: Make predicts pure functions. Predicate purity: A predicate is a function object that returns a yes/no answer, typically as a bool value. A function is pure in the mathematical sense if its results depend only on its arguments (note that this use of "pure" has nothing to do with pure virtual functions). Don't allow predicates to hold or access state that affects the result of their operator() , including both member and global state. Prefer to make operator() a const

Collection及其师傅Iterable

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【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> 上一节我们缕清了Collection家族的关系，接下来我们就来看看这个家族的创始者及其师傅。 1. 师傅Iterable Iterable是一个接口类，先看看接口里面的方法：其中第二个和第三个方法，都是java8新增的，看源码会发现，java8后，可以在接口里面定义默认（关键字default）的方法（必须实现，可以空实现），而且实现类中还可以重写default方法，这样一来有点类似抽象类，只不过接口类用来授艺，抽象类用来遗传。最终给我们代码的迭代带来很大便利。 Iterable里面最主要的当然迭代器Iterator，Iterator本身是接口，这么说来接口师傅（水平有限）传授的都是大道的终极要义，功夫还是得弟子苦练。后来师傅能力提升（java8来了），可以给弟子大道的精华（default方法），让弟子可以毫不费力直接领悟，甚至弟子还可以加以创新（重写），但是要注意多接口实现造成的默认方法冲突问题（冲突很容易解决，就不多说）。关于Iterator在子类的实现可以查看ArrayList源码，很简单，只是大家用得多的是next()方法，不知有没有注意到previous()方法。值得一提的是在Iterator接口里面新增了默认方法：forEachRemaining方法，允许传入一个行为