builder

问题 This might be quite easy but have no idea how to. I have a table that can have repeated values for a particular non-key column field. How do I write a SQL query using Query Builder or Eloquent that will fetch rows with distinct values for that column? Note that I am not fetching that column only, it is in conjunction with other column values, so distinct() might not really work. So that question basically can be how to specify the column that I want to be distinct in a query now that distinct

问题 Often I find it tedious to implement the builder pattern with pre-java-8 setups. There is always lots of nearly duplicated code. The builder itself could be considered boilerplate. In fact there are code duplicate detectors, that would consider nearly each method of a builder made with pre-java-8 facilities as a duplicate of every other method. So considering the following class and it's pre-java-8 builder: public class Person { private String name; private int age; public String getName() {

问题 To date I use the following implementation of the builder pattern (as opposed to the implementation described here): public class Widget { public static class Builder { public Builder(String name, double price) { ... } public Widget build() { ... } public Builder manufacturer(String value) { ... } public Builder serialNumber(String value) { ... } public Builder model(String value) { ... } } private Widget(Builder builder) { ... } } This works well for most situations I've encountered where I

问题 To date I use the following implementation of the builder pattern (as opposed to the implementation described here): public class Widget { public static class Builder { public Builder(String name, double price) { ... } public Widget build() { ... } public Builder manufacturer(String value) { ... } public Builder serialNumber(String value) { ... } public Builder model(String value) { ... } } private Widget(Builder builder) { ... } } This works well for most situations I've encountered where I

问题 I have an object hierarchy that increases in complexity as the inheritance tree deepens. None of these are abstract, hence, all of their instances serve a, more or less sophisticated, purpose. As the number of parameters is quite high, I would want to use the Builder Pattern to set properties rather than code several constructors. As I need to cater to all permutations, leaf classes in my inheritance tree would have telescoping constructors. I have browsed for an answer here when I hit some

问题 In builder design pattern, is method buildpart() a factory method? (For comparison, an abstract factory is a collection of factory methods.) Why are they (not) factory methods? For clarification, could you also provide the definition of a factory method? An example for buildpart() from Design Patterns by Gamma et al is: void StandardMazeBuilder::BuildMaze () { _currentMaze = new Maze; } 回答1: A factory method creates a concrete object/product, usually with the new keyword, and returns that

问题 I've been studying design patterns with a study group recently, and have come to understand that the builder pattern can be very useful for creating complex objects that are made up of many (potentially optional) parts. However, is there ever a point where the builder is doing too much? Let's say we have a class that has many many different combinations of objects, is there another pattern that may be better suited for that instead of making dozens of different builders? Is it possible to

问题 From Design Pattern by Gang of Four, Example: Why doesn't the interface Builder have a method GetResult() , which is overridden in the concrete class ConcreteBuilder ? In the example, the concrete builders have GetXXX() methods, where XXX is different for different concrete builders, which doesn't promote "programming to interface" at all. Is this "omission" deliberate in the builder pattern? 回答1: Yes, the omission is deliberate. The book addresses it directly. Why no abstract class for

问题 I am trying to implement builder pattern with fluent interface for building the objects in C++. I want the builder to follow CRTP pattern. In Java, I would do something similar to the below code. How do I do the same in C++? The below is some java code that has a base class and a derived class. The derived class's builder inherits the base class's builder.. // Base class public abstract class BaseClass { private final int base_class_variable; BaseClass(final Builder <?> builder) { this.base

问题 I am building an object with a simple loop: WebTarget target = getClient().target(u); for (Entry<String, String> queryParam : queryParams.entrySet()) { target = target.queryParam(queryParam.getKey(), queryParam.getValue()); } I want to do the same thing using the Java8 Stream API but I cannot figure out how to do it. What makes me struggle is that target is reassigned every time, so a simple .forEach() will not work. I guess I need to use a .collect() or reduce() since I am looking for a