Grails - hasMany & belongTo

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

class Book {
    String title
    static belongsTo = [author: Author]
    static constraints = {
    }
    static mapping = {
        author cascade: ‘all‘
    }
}

// 自动创建出来的表结构
CREATE TABLE
    author
    (
        id BIGINT NOT NULL,
        version BIGINT NOT NULL,
        name CHARACTER VARYING(255) NOT NULL,
        PRIMARY KEY (id)
    );

CREATE TABLE
    book
    (
        id BIGINT NOT NULL,
        version BIGINT NOT NULL,
        title CHARACTER VARYING(255) NOT NULL,
        author_id BIGINT NOT NULL,
        PRIMARY KEY (id),
        CONSTRAINT fkklnrv3weler2ftkweewlky958 FOREIGN KEY (author_id) REFERENCES "author" ("id")
    );