# Hibernate

## 以程式初始化

版本：5+

```java
StandardServiceRegistry registry = new StandardServiceRegistryBuilder()
    .configure()    //非必須，有掛的話在 classpath 當中就得要有 hibernate.cfg.xml
    .applySetting(AvailableSettings.DRIVER, "org.h2.Driver")
    //apply... apply... apply...
    .build()
;

MetadataSources sources = new MetadataSources(registry)
    .addAnnotatedClass(Foo.class)    //等同 cfg.xml <mapping class="PACKAGE.Foo" />
    //目前看不出 Hibernate 有提供「載入指定 package 下所有 class」的方式... ＝＝"
;

SessionFactory sessionFactory  = sources.getMetadataBuilder().build()
    .getSessionFactoryBuilder().build();
```

## Entity 的哏

資料庫的欄位沒辦法直接 mapping 到 Java class，例如資料庫儲存的是「Y/N」實際上希望對應到 boolean。 目前發現兩招，第一招是掛 `@Basic`，例如

```
@Basic
private String enabled;

public Boolean getEnabled() {
    return "TRUE".equalsIgnoreCase(enabled);
}

public void setEnabled(Boolean enabled) {
    this.enabled = enabled ? "TRUE" : "FALSE";
}
```

第二招是掛 `@Converter`，還沒試過。 [reference](http://stackoverflow.com/questions/1154833/configure-hibernate-using-jpa-to-store-y-n-for-type-boolean-instead-of-0-1)

如果希望新增資料的時候，某個欄位直接使用 DB 預設值（而不是 entity field 當下的值）， 在 `@Column` 裡頭加上 `insertable = false`：

```
@Column(insertable = false)
private Date createDate;
```

## HQL 的哏

Session.createQuery() 裡頭的字串邏輯：

* 不是用 DB 的 table / column name，而是用 Java 的 class / field name
* parameter name 用 `:` 開頭，實際參數不需要 `:`

### Sub Query ##\#

在 `IN` / `NOT IN` 使用 sub query 的時候，如果這樣寫

```
FROM foo WHERE id NOT IN (FROM wtf)
```

`foo.id` 會比對的是 `wtf.id`。如果要作 NOT IN 的是 `wtf.fooId`，要這樣寫

```
FROM foo WHERE id NOT IN (SELECT fooId FROM wtf)
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://www.psmonkey.org/ruan-ti-kai-fa/java/hibernate.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.