# [Grails] GORM

參考資料 [GORM for Hibernate](http://gorm.grails.org/6.1.x/hibernate/manual/#domainClasses)

通過規約，Grails 會自動把放在 `racetrack/grails-app/domain` 里面的類識別為 domain class，且知道 domain class 需持久化

---
## Grails 數據庫規約
* DB table 名與 domain class 名一致。
* coloum name 和 properties name 一致。
* 對於多單詞組成的 properties name 以底線分開單詞
例：maxRunners 跟 max_runners 對應。
* id 是 PK，被定義為 auto_increment。
* 每個 Grails domain class 都需要 id 和 version 屬性，所以，在編譯期 GORM 會把它們注入到 class 里面。
註：version 屬性為 Hibernate 支持事務管理和樂觀鎖用

## Domain Modelling in GORM
### Many-to-one & one-to-one

Example

class Face {
    Nose nose
}

class Nose {
}

#### ``belongsTo``
Tells GORM to cascade commands: e.g., delete this object if the "parent" is deleted.

static	belongsTo = []

Example:

class Face {
    Nose nose
}

class Nose {
    static belongsTo = [face:Face]
}

#### `` hasOne``
Tells GORM to associate another domain object as an owner in a 1-1 mapping.

static	hasOne = []	

Example

class Face {
    static hasOne = [nose:Nose]
    static constraints = {
        nose unique: true
    }
}

class Nose {
    Face face
}

:::info
**hasOne** 僅在雙向關係中運作
:::
### One-to-many
#### `` hasMany``
Tells GORM to associate other domain objects for a 1-n or n-m mapping

static	hasMany	= [productSpecs:ProductSpec]

Example

class Author {
    static hasMany = [books: Book]
    String name
}

class Book {
    String title
}

可以使用 ```cascade``` 刪除關聯的項目

class Book {
    String name
    static hasMany = [reviews: Review]
	static mappping = {
        reviews cascade: 'all-delete-orphan'
    }
}

class Review {
    String author
    String quote
    static belongsTo = [book: Book]
}

#### ```cascade``` 可使用的參數一覽

- ```merge``` - merges the state of a detached association
- ```save-update``` - cascades only saves and updates to an association
- ```delete``` - cascades only deletes to an association
- ```lock``` - useful if a pessimistic lock should be cascaded to its associations
- ```refresh``` - cascades refreshes to an association
- ```evict``` - cascades evictions (equivalent to discard() in GORM) to associations if set
- ```all``` - cascade all operations to associations
- ```all-delete-orphan``` - Applies only to one-to-many associations and indicates that when a child is removed from an association then it should be automatically deleted. Children are also deleted when the parent is.

#### ```mappedBy```
Specifies which property should be used in a mapping

static	mappedBy = []	

如果一對多的多那方具有兩個相同類型的屬性，則必須使用 mappedBy 指定要映射的集合

class Airport {
    static hasMany = [flights: Flight]
    static mappedBy = [flights: "departureAirport"]
}

class Flight {
    Airport departureAirport
    Airport destinationAirport
}

### Many-to-many
Grails 藉由在關係的雙方定義 ```hasMany```，以及在擁有此多對多關係的那方定義 ```belongsTo``` 建立多對多關係。

class Book {
    static belongsTo = Author
    static hasMany = [authors:Author]
    String title
}

class Author {
    static hasMany = [books:Book]
    String name
}

___

## Validation & Constraints
Grails **validation** capability is built on Spring's Validator API and data binding capabilities. However Grails takes this further and provides a unified way to define validation constraints with its **constraints** mechanism.

Most commonly they are applied to [domain classes](https://docs.grails.org/3.0.x/guide/single.html#GORM), however [URL Mappings](https://docs.grails.org/3.0.x/guide/single.html#urlmappings) and [Command Objects](https://docs.grails.org/3.0.x/guide/single.html#commandObjects) also support constraints.

---

### Declaring Constraints
#### Example for domain class constraints

class User {
    String login
    String password
    String email
	
static constraints = {
    login size: 5..15, blank: false, unique: true
    password size: 5..15, blank: false
    email email: true, blank: false
    }
}

#### Example for ==Referencing domain class properties== from constraints

class Product {

/* Default (injected) attributes of GORM */
Long	id
Long	version

StationSpec startStationSpec
StationSpec endStationSpec
BookingSpec bookingSpec

static	constraints = {
        bookingSpec(nullable:true)
	startStationSpec(nullable: true)
	endStationSpec(nullable: true)
		
    }
	
}
	

:::warning
By default, all domain class properties are not nullable (i.e. they have an implicit nullable: false constraint).
:::
---
### GORM & Constraints
假設有個屬性如下所示的 class

String name
String description

預設情況下，Grails 在 MySQL 中會將其定義為

| Column | Data Type |
| ----------- | ------------ |
| name | varchar(255) |
| description | varchar(255) |

但 description 的商業邏輯定義可能是「最大為 1000 字」，
若是如此，在創建資料表時可改為以下設定方式。

| Column | Data Type |
| ----------- | --------- |
| description | TEXT |

並加上 constraints 確保不會超過 1000 字

static constraints = {
    description maxSize: 1000
}

To use GORM 7.0.4 for Hibernate in Grails 3 you can specify the following configuration in build.gradle:

dependencies {
    compile "org.grails.plugins:hibernate5:7.0.4"
    compile "org.hibernate:hibernate-ehcache"
}

___
## Dependency configurations

>`compile`、`runtime`、`compileOnly`、`testCompile`、`testRuntime`、`testCompileOnly`...etc.

**`compile`** – 專案在編譯的階段就需要這些相依函式庫內容，這包含相依庫的子依賴，這些內容最後都會加到 classpath。
例如 Spring、Hibernate 的相依庫。

**`runtime`** – 繼承於 `compile`。專案在執行的時候會需要這些相依庫。例如 MySQL driver 的相依庫。

註：假設專案使用一個相依 A，而 A 又相依 B，專案編譯階段只需要 A，但執行階段時其實是需要 A 和 B，這是為何配置 compile 的相依可以被 runtime 看見，但反過來卻不一定正確。

**`compileOnly`** -繼承於 compile。這些相依庫基本上只有專案編譯的階段被使用，專案執行階段的時候不被使用，這些內容最後不會被加入到 `runtime` 的 `classpath` 裡。像 `source-only annotations`。

註：某相依庫的 API 在編譯時段被需要，但實作的內容則是由執行時的應用程式、其他相依、環境所提供。

參考資料：[Gradle相依性配置筆記](https://www.ajoshow.com/2017/08/06/20170806/)