使用Rails，我如何设置我的主键不是一个整数类型的列？ [英] Using Rails, how can I set my primary key to not be an integer-typed column?

问题描述

我使用Rails迁移来管理数据库模式，我创建了一个简单的表，其中我想使用非整数值作为主键（特别是字符串）。为了抽象出我的问题，让我们假设有一个表 employees ，其中雇员通过字母数字字符串来标识。 134SNW。

I'm using Rails migrations to manage a database schema, and I'm creating a simple table where I'd like to use a non-integer value as the primary key (in particular, a string). To abstract away from my problem, let's say there's a table employees where employees are identified by an alphanumeric string, e.g. "134SNW".

我已经尝试在迁移中创建表格，如下所示：

I've tried creating the table in a migration like this:

create_table :employees, {:primary_key => :emp_id} do |t|
    t.string :emp_id
    t.string :first_name
    t.string :last_name
end

这给我的是什么似乎完全忽略了 t.string：emp_id 行，并使它成为一个整数柱。有没有其他方法来让rails生成PRIMARY_KEY约束（我使用PostgreSQL）为我，而不必写在执行调用？

What this gives me is what seems like it completely ignored the line t.string :emp_id and went ahead and made it an integer column. Is there some other way to have rails generate the PRIMARY_KEY constraint (I'm using PostgreSQL) for me, without having to write the SQL in an execute call?

注意：我知道最好不要使用字符串列作为主键，所以请没有答案只是说添加一个整数主键。我可以添加一个，但这个问题仍然有效。

NOTE: I know it's not best to use string columns as primary keys, so please no answers just saying to add an integer primary key. I may add one anyway, but this question is still valid.

推荐答案

不幸的是，我确定它不可能不使用执行。

Unfortunately, I've determined it's not possible to do it without using execute.

通过检查ActiveRecord源代码，我们可以找到 create_table 的代码：

By examining the ActiveRecord source, we can find the code for create_table:

在 schema_statements.rb code> ：

In schema_statements.rb:

def create_table(table_name, options={})
  ...
  table_definition.primary_key(options[:primary_key] || Base.get_primary_key(table_name.to_s.singularize)) unless options[:id] == false
  ...
end

所以我们可以看到，当你尝试在 create_table 选项，它创建具有指定名称的主键（或者如果没有指定名称，则 id ）。它通过调用可以在表定义块中使用的相同方法来执行此操作： primary_key 。

So we can see that when you try to specify a primary key in the create_table options, it creates a primary key with that specified name (or, if none is specified, id). It does this by calling the same method you can use inside a table definition block: primary_key.

href =https://github.com/rails/rails/blob/a63f7a136401b59db52fb802180f6c9793d83bc2/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb#L89 =noreferrer> schema_statements.rb ：

In schema_statements.rb:

def primary_key(name)
  column(name, :primary_key)
end

这只是创建一个指定名称为：primary_key 。这在标准数据库适配器中设置如下：

This just creates a column with the specified name of type :primary_key. This is set to the following in the standard database adapters:

PostgreSQL: "serial primary key"
MySQL: "int(11) DEFAULT NULL auto_increment PRIMARY KEY"
SQLite: "INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL"

解决方法

因为我们坚持使用这些作为主键类型，我们必须使用 execute 创建不是整数的主键（PostgreSQL的 serial 是使用序列的整数）：

The workaround

Since we're stuck with these as the primary key types, we have to use execute to create a primary key that is not an integer (PostgreSQL's serial is an integer using a sequence):

create_table :employees, {:id => false} do |t|
  t.string :emp_id
  t.string :first_name
  t.string :last_name
end
execute "ALTER TABLE employees ADD PRIMARY KEY (emp_id);"

并且 Sean McCleary提到，你的ActiveRecord模型应该设置主键 set_primary_key ：

And as Sean McCleary mentioned, your ActiveRecord model should set the primary key using set_primary_key:

class Employee < ActiveRecord::Base
  set_primary_key :emp_id
  ...
end

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