I'm writing a migration that involves a foreign key. Looking at my colleagues code, I see that he has added the line: t.reference :tablename, index: true
我正在写一个涉及外键的迁移。看着我的同事代码，我看到他添加了一行：t.reference：tablename，index：true
The t.reference part makes sense, but I don't know what index: true means. Can anyone tell me? I haven't been able to find that in the docs.
t.reference部分是有道理的，但我不知道索引：true表示。有人能告诉我吗？我无法在文档中找到它。
Note: This is not a duplicate of: Rails ActiveRecord::Migration what is the difference between index: true and add_index? Which only diffs the two, but doesn't explain what they do.
注意：这不是重复：Rails ActiveRecord :: Migration index：true和add_index有什么区别？这只是两者的区别，但没有解释他们做了什么。
2 个解决方案
#1
16
index: true adds a database index to the referenced column. For example, if creating a :products table:
index：true将数据库索引添加到引用的列。例如，如果创建：products表：
create_table :products do |t|
t.references :user, index: true
end
That will create a user_id column in the products table. It will also create a non-unique index on the user_id column, named index_products_on_user_id.
这将在products表中创建user_id列。它还将在user_id列上创建一个名为index_products_on_user_id的非唯一索引。
#2
0
well, when you create this add_reference thing you are saying to rails to add a user_id within "product table". i think the id's are useful to connect differents tables.
好吧，当你创建这个add_reference的东西时，你要告诉rails在“产品表”中添加一个user_id。我认为id对连接不同的表很有用。
#1
16
index: true adds a database index to the referenced column. For example, if creating a :products table:
index：true将数据库索引添加到引用的列。例如，如果创建：products表：
create_table :products do |t|
t.references :user, index: true
end
That will create a user_id column in the products table. It will also create a non-unique index on the user_id column, named index_products_on_user_id.
这将在products表中创建user_id列。它还将在user_id列上创建一个名为index_products_on_user_id的非唯一索引。
#2
0
well, when you create this add_reference thing you are saying to rails to add a user_id within "product table". i think the id's are useful to connect differents tables.
好吧，当你创建这个add_reference的东西时，你要告诉rails在“产品表”中添加一个user_id。我认为id对连接不同的表很有用。