ruby-on-rails - Rails:PG::NotNullViolation:错误:列 "id"中的空值违反了非空约束

Question

这是在 rails 3.2.12 和 pg 9.3 上将记录保存到 postgres 数据库时的错误:

ActiveRecord::StatementInvalid (PG::NotNullViolation: ERROR:  null value in column "id" violates not-null constraint
: INSERT INTO "sw_module_infox_module_infos" ("about_controller", "about_init", "about_log", "about_misc_def", "about_model", "about_onboard_data", "about_subaction", "about_view", "about_workflow", "active", "api_spec", "category_id", "created_at", "last_updated_by_id", "module_desp", "name", "submit_date", "submitted_by_id", "updated_at", "version", "wf_state") VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14, $15, $16, $17, $18, $19, $20, $21) RETURNING "id"):
  activerecord (3.2.12) lib/active_record/connection_adapters/postgresql_adapter.rb:1166:in `get_last_result'
  activerecord (3.2.12) lib/active_record/connection_adapters/postgresql_adapter.rb:1166:in `exec_cache'

该表到目前为止工作正常(今天出错前保存了大约 50 条记录)。在 pgadmin 中打开 pg 表后。我们发现表中的 id 是 integer。我们还发现其他表上的 Id 是 serial。看来 id 应该是 serial 这样它就可以自动递增了。如果是，那么如何将 id 列从 integer 转换为 serial？如果不是，那么如何解决这个问题？

Answer 1

The data types smallserial, serial and bigserial are not true types, but merely a notational convenience for creating unique identifier columns (similar to the AUTO_INCREMENT property supported by some other databases).

如果您的列是一个整数，您不能将它转换为序列，但您可以模仿，PostgreSQL 会做的，只是就像您使用序列号创建表格一样:

CREATE SEQUENCE tablename_colname_seq;
ALTER TABLE tablename ALTER COLUMN colname SET DEFAULT nextval('tablename_colname_seq'::regclass);
ALTER SEQUENCE tablename_colname_seq OWNED BY tablename.colname;