更新 Rails 4 和 PostgreSQL json 列中的单个键/值对？
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Updating a single key/value pair in a Rails 4 and PostgreSQL json column?
提问by Randy Burgess
I have a rather large json document that I have to store in a field for each Evaluation instance in my app. The over time, certain actions on the app will require me to change various key/value pairs in the document. The Rails 4 and PostgreSQL json data type seems ideal for this problem, but I cannot get changes to commit to the database.
我有一个相当大的 json 文档，我必须将其存储在应用程序中每个评估实例的字段中。随着时间的推移，应用程序上的某些操作将需要我更改文档中的各种键/值对。Rails 4 和 PostgreSQL json 数据类型似乎非常适合解决此问题，但我无法更改以提交到数据库。
Here's an abbreviated workflow:
这是一个简短的工作流程：
I have a json file that I import into a field for each Evaluation record:
我有一个 json 文件，我将其导入到每个评估记录的字段中：
// example.json
{ "question_1":"no" }
I create a record and import the json:
我创建一个记录并导入 json：
>> evaluation = Evaluation.create assessments: File.read("example.json")
>> evaluation.assessments = File.read("#{Rails.root}/example.json")
=> "{ \"question_1\":\"no\" }"
Calling on the assessments field seems to work fine:
调用评估领域似乎工作正常：
>> evaluation.assessments
=> {"question_1"=>"no"}
OR
>> evaluation.assessments["question_1"]
=> "no"
Example 1
示例 1
Changing the json isn't working too well. This doesn't actually commit anything:
更改 json 的效果不太好。这实际上并没有提交任何东西：
>> evaluation.assessments["question_1"] = "yes"
=> "yes"
>> evaluation.assessments["question_1"]
=> "yes"
>> evaluation.save
(0.3ms) BEGIN
(0.2ms) COMMIT
=> true
Example #2
示例#2
Replacing with a completely new object doescommit:
用一个全新的对象替换确实提交：
>> evaluation.assessments = {"question_1"=>"yes"}
=> {"question_1"=>"yes"}
>> evaluation.save
(0.3ms) BEGIN
SQL (0.7ms) UPDATE "evaluations" SET "assessments" = , "updated_at" = WHERE "evaluations"."id" = 1 [["assessments", "{\"question_1\":\"yes\"}"], ["updated_at", "2014-08-21 00:52:03.581817"]]
(3.8ms) COMMIT
=> true
- What am I doing wrong in Example #1?
- Why won't the database commit the change I made to the
evaluation.assessmentcolumn when I call it, change the value, and call save on the instance?
- 我在示例 #1 中做错了什么？
evaluation.assessment当我调用它、更改值并在实例上调用 save 时，为什么数据库不会提交我对列所做的更改？
回答by Randy Burgess
This ended up being an easy fix due to a known bug related to ActiveRecord not knowing the changed attribute is dirty:
由于与 ActiveRecord 相关的已知错误不知道更改的属性是脏的，这最终是一个简单的修复：
https://github.com/rails/rails/issues/6127
https://github.com/rails/rails/issues/6127
Here's the solution:
这是解决方案：
>> evaluation.assessments["question_1"] = "yes"
=> "yes"
>> evaluation.assessments_will_change!
>> evaluation.save
(1.1ms) BEGIN
SQL (1.6ms) UPDATE "evaluations" SET "assessments" = , "updated_at" = WHERE "evaluations"."id" = 4 [["assessments", "{\"question_1\":\"yes\"}"], ["updated_at", "2014-08-21 01:59:47.331216"]]
(2.5ms) COMMIT
=> true
