Grails：获取“字段 XXX 没有默认值”

Question

我遇到了一个由两个域类之间的多对多关系引起的奇怪错误。课程如下。当我尝试保存 NoteParagraph 对象时，我不会立即收到错误消息：

NoteParagraph np = new NoteParagraph(number: noteNumber, content: noteText)
note.addToChildParagraphs(np).save()

但是，在下一个 .save() 操作（在不相关的对象上）时，我收到以下错误堆栈跟踪：

Field 'note_paragraph_id' doesn't have a default value. Stacktrace follows:
java.sql.SQLException: Field 'note_paragraph_id' doesn't have a default value
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:998)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3847)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3783)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2447)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2594)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2545)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1901)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2113)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2049)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2034)
at org.grails.datastore.gorm.GormStaticApi$_methodMissing_closure2.doCall(GormStaticApi.groovy:102)

这是我的课程：

class NoteParagraph {

    String number
    String content
    Note parentNote

    Date dateCreated
    Date lastUpdated

    static belongsTo = Note

    static hasMany = [
        childNotes: Note
    ]

    static constraints = {
    }

    static mapping = {
        content type:'text'
    }
}

第二个：

class Note {

    Integer noteType
    Integer parentType
    Integer parentId
    String heading

    Date dateCreated
    Date lastUpdated

    static hasMany = [
        childParagraphs: NoteParagraph
    ]

    static constraints = {

    }

    static mapping = {
        heading type:'text'
    }
}

我已尝试按照其他线程的建议删除并重新创建我的数据库，但没有帮助。

Answer 1

修复：

class NoteParagraph {

    String number
    String content

    Date dateCreated
    Date lastUpdated

    static belongsTo = [parentNote: Note]

    static hasMany = [
        childNotes: Note
    ]

    static constraints = {
    }

    static mapping = {
        content type:'text'
    }
}

当您尝试将 NoteParagraph 添加到 Note 时，NoteParagraph 实例不是持久的（它已创建但尚未保存在 db 中）。

尝试改变：

NoteParagraph np = new NoteParagraph(number: noteNumber, content: noteText)
note.addToChildParagraphs(np).save()

到：

note.save(flush: true) //add also this, if note is not persisted
NoteParagraph np = new NoteParagraph(number: noteNumber, content: noteText, parentNote: note).save(flush: true)
note.addToChildParagraphs(np).save()