如何在连接表中添加值?

Question

我创建了两个表，一个是Category，一个是Manufacturer，它们的关系是多对多，所以我使用连接表，我分别向两个表中插入值。现在我想通过id连接两个表，但是我做不到，你能帮我....吗当我尝试在连接表中插入值时，给出一个异常，下面是异常:

    Cannot invoke method addToManufacturers() on null object. Stacktrace follows:
java.lang.NullPointerException: Cannot invoke method addToManufacturers() on null object

这是Category

的域类

static hasMany    =  [manufacturers: Manufacturer]
static constraints = {
    name     blank: false, size: 0..60, unique: false
}
static mapping = {
    table 't01i001'
    id      column: 'f_category_id'
    name    column: 'f_name', length: 30     
    version column: 'f_revision'
    manufacturers joinTable: [name: 't01j001', key: 'k_category_id', column: 'k_manufacturer_id']
}

这是我的域类制造商

static belongsTo  =  Category 
static hasMany    =  [categories: Category]
static constraints = {
    name     blank: false, size: 0..60, unique: false
}
static mapping = {
    table 't01i002'
    id        column: 'f_manufacturer_id'
    name      column: 'f_name',         length: 30
    version   column: 'f_revision'
    categories joinTable: [name: 't01j001', key: 'k_manufacturer_id', column: 'k_category_id']
}

添加我的控制器，我试图插入

def manuInsertInCat(){
    def message, flag,count=0,categories = []
    int  catid  = params.containsKey("catid") ? params.catid : '0' 
    int  manuid = params.containsKey("manuid") ? params.manuid : '0' 
    def category    = Category.get(catid);
    def manufacture = Manufacturer.get(manuid)
    category.addToManufacturers(manufacture)
    message = "Successfully Loaded"
    count++
    flag =true
    render Category.getJsonData(categories, count, flag, message)        
}

Answer 1

最后我通过这个过程完成了我的工作，效果很好。

def catInsertInManu(){
    def message, flag,count=0,manufacturers = []
    String  catid  = params.containsKey("catid") ? params.catid : '0' 
    String  manuid = params.containsKey("manuid") ? params.manuid : '0' 
    def category    = Category.get(catid)
    def manufacture = Manufacturer.get(manuid)
    manufacture.addToCategories(category)
    def m01i001001s = []
    manufacture.categories.each{ cat ->
        m01i001001s << [id:cat.id, name:cat.name]
    }
    manufacturers << [id: manufacture.id, name:manufacture.name, m01i001001s:m01i001001s]
    message = "Successfully Loaded"
    count++
    flag =true        
    render Manufacturer.getJsonData(manufacturers, count, flag, message)        
}