1. 沙盒(sandbox)模式

  • 可用沙盒模式进行测试，rails c --sandbox
    # Any modifications you make will be rolled back on exit
  • sandbox 模式，会模拟 增删改 数据以及关联关系，并不会提交事务，所以不会插入到库， 所有的操作都会在退出的时候 rollback

2. delete_all

  • delete_all 不会走 callback, 会直接生成一条 delete SQL 语句，比如：
 Project.where(id: 1).delete_all
# =>
# DELETE FROM "PROJECTS" WHERE "PROJECTS"."ID" = :a1  [["id", 1]]

3. destroy_all

  • destroy_all 会走 callback（相关的数据也都删除）, 会生成多条 delete SQL 语句
Project.where(id: [1, 2]).destroy_all
# =>
# DELETE FROM "PROJECTS" WHERE "PROJECTS"."ID" = :a1  [["id", 1]]
# DELETE FROM "PROJECTS" WHERE "PROJECTS"."ID" = :a1  [["id", 2]]
  • 同时也会把模型中 has_many 配置了 dependent: :delete_all 或者 dependent: :destroy 的给删除掉

3.1. destroy_all 之 has_many 中的参数 dependent: :delete_all

  • dependent: :delete_all 会生成一条 delete SQL 语句, has_many 关系数据全部删除, has_many关联的模型不会走 callback
Project.where(id: [1, 2]).destroy_all
# =>
# DELETE FROM "PROJECTS" WHERE "PROJECTS"."ID" = :a1  [["id", 1]]
# DELETE FROM "PROJECT_EXTRA_PROPERTIES" WHERE "PROJECT_EXTRA_PROPERTIES"."PROJECT_ID" = :a1  [["project_id", 1]]
# DELETE FROM "PROJECTS" WHERE "PROJECTS"."ID" = :a1  [["id", 2]]
# DELETE FROM "PROJECT_EXTRA_PROPERTIES" WHERE "PROJECT_EXTRA_PROPERTIES"."PROJECT_ID" = :a1  [["project_id", 2]]

3.2. destroy_all 之 has_many 中的参数 dependent: :destroy

  • dependent: :destroy 会生成多条 delete SQL 语句, has_many 全部删除, 会走 callback（相关的数据也都删除）
Project.where(id: [1, 2]).destroy_all
# =>
# DELETE FROM "PROJECTS" WHERE "PROJECTS"."ID" = :a1  [["id", 1]]
# 多条
# DELETE FROM "PROJECT_EXTRA_PROPERTIES" WHERE "PROJECT_EXTRA_PROPERTIES"."ID" = :a1  [["id", 1804]]
# DELETE FROM "PROJECT_EXTRA_PROPERTIES" WHERE "PROJECT_EXTRA_PROPERTIES"."ID" = :a1  [["id", 1803]]
# DELETE FROM "PROJECTS" WHERE "PROJECTS"."ID" = :a1  [["id", 2]]
# 多条
# DELETE FROM "PROJECT_EXTRA_PROPERTIES" WHERE "PROJECT_EXTRA_PROPERTIES"."ID" = :a1  [["id", 1806]]
# DELETE FROM "PROJECT_EXTRA_PROPERTIES" WHERE "PROJECT_EXTRA_PROPERTIES"."ID" = :a1  [["id", 1805]]

4. 特别注意：has_many.delete_all

`Project.find(1).project_extra_properties.delete_all`, 并不一定会生成一条 `delete SQL` 语句

4.1. 如果你的 has_many 配置了 dependent 参数 dependent: :destroy 或者 dependent: :delete_all

会生成一条 delete SQL 语句

# DELETE FROM "PROJECT_EXTRA_PROPERTIES" WHERE "PROJECT_EXTRA_PROPERTIES"."PROJECT_ID" = :a1  [["project_id", 1]]

4.2. 如果你的 has_many 没有配置 dependent: :destroy 或者 dependent: :delete_all

  • 而是会生成一条 update SQL 语句

#  UPDATE "PROJECT_EXTRA_PROPERTIES" SET "PROJECT_EXTRA_PROPERTIES"."PROJECT_ID" = NULL WHERE "PROJECT_EXTRA_PROPERTIES"."PROJECT_ID" = :a1  [["project_id", 1]]


# select * from projects where project_name = NULL
# select * from projects where project_name is NULL

以上两条语句查询出的结果不一样 project_name = NULL 永远不会为 true

用 project_name is NULL 代替