Rails和Postgres，按hstore分组

Question

I have an 'Audit' model with name:string and data:hstore attributes - as follows:

#<Audit 
id: 1, 
name: "my audit", 
data: {"publisher"=>"some publisher",  "display_version"=>"17.012.20098"}, 
created_at: "2017-10-10 13:09:56", 
updated_at: "2017-10-10 13:09:56">

I want to produce a report that contains 3 columns: name, display_version, count

To achieve this I assume that I need to group by "name" and "data -> 'display_version'"

I am struggling with the query and AR syntax.

What I have so far is:

Parent.audits.group(:name, :data -> 'display_version)'

Even this doesn't work. Can someone help? I have searched for examples without any luck.

Answer 1

You can pass a string containing the SQL grouping expression to group so you could say:

Parent.audits.group(%q{name, data -> 'display_version'})

or:

Parent.audits.group(%q{audits.name, audits.data -> 'display_version'})

And then you could throw a #count call on the end to get the data you want:

Parent.audits.group(%q{name, data -> 'display_version'}).count

Answer 2

Use jsonb instead of hstore (for a variety of reasons)

'Audit' model with name:string and data:jsonb

Audit.rb

store_accessor :data, :publisher, :display_version

Then try:

Parent.audits.pluck(:name, :publisher, :display_version)

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Good Resource on JSONB and Postgresql

hstore columns don't allow a nested structure; they also store all values as strings, which will require type coercion on both database and application layers. With json/jsonb columns you don't have this problem; numbers (integers/float), booleans, arrays, strings and nulls are accepted, and you can even nest structures in any way you want.

The recommendation is that you stop using hstore in favor of jsonb; just remember that you have to use PostgreSQL 9.4+ for this to work.