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* pr/599:
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Updating README with solution for DISTINCT issues
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Jon Atack 2015-12-05 23:46:54 +01:00
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@ -93,22 +93,6 @@ If you're coming from MetaSearch, things to note:
ActiveRecord::Relation in the case of the ActiveRecord adapter) via a call to
`Ransack#result`.
4. If passed `distinct: true`, `result` will generate a `SELECT DISTINCT` to
avoid returning duplicate rows, even if conditions on a join would otherwise
result in some. It generates the same SQL as calling `uniq` on the relation.
Please note that for many databases, a sort on an associated table's columns
may result in invalid SQL with `distinct: true` -- in those cases, you're on
your own, and will need to modify the result as needed to allow these queries
to work.
If `distinct: true` or `uniq` is causing invalid SQL, another way to remove
duplicates is to call `to_a.uniq` on the collection at the end (see the next
section below) -- with the caveat that the de-duping is taking place in Ruby
instead of in SQL, which is potentially slower and uses more memory, and that
it may display awkwardly with pagination if the number of results is greater
than the page size.
####In your controller
```ruby
@ -370,6 +354,58 @@ information about `ransacker` methods can be found [here in the wiki]
(https://github.com/activerecord-hackery/ransack/wiki/Using-Ransackers).
Feel free to contribute working `ransacker` code examples to the wiki!
### Problem with DISTINCT selects
If passed `distinct: true`, `result` will generate a `SELECT DISTINCT` to
avoid returning duplicate rows, even if conditions on a join would otherwise
result in some. It generates the same SQL as calling `uniq` on the relation.
Please note that for many databases, a sort on an associated table's columns
may result in invalid SQL with `distinct: true` -- in those cases, you will
will need to modify the result as needed to allow these queries to work.
For example, you could call joins and includes on the result which has the
effect of adding those tables columns to the select statement, overcoming
the issue, like so:
```ruby
def index
@q = Person.ransack(params[:q])
@people = @q.result(distinct: true)
.includes(:articles)
.joins(:articles)
.page(params[:page])
end
```
If the above doesn't help, you can also use ActiveRecord's `select` query
to explicitly add the columns you need, which brute force's adding the
columns you need that your SQL engine is complaining about, you need to
make sure you give all of the columns you care about, for example:
```ruby
def index
@q = Person.ransack(params[:q])
@people = @q.result(distinct: true)
.select('people.*, articles.name, articles.description')
.page(params[:page])
end
```
A final way of last resort is to call `to_a.uniq` on the collection at the end
with the caveat that the de-duping is taking place in Ruby instead of in SQL,
which is potentially slower and uses more memory, and that it may display
awkwardly with pagination if the number of results is greater than the page size.
For example:
```ruby
def index
@q = Person.ransack(params[:q])
@people = @q.result.includes(:articles).page(params[:page]).to_a.uniq
end
```
### Authorization (whitelisting/blacklisting)
By default, searching and sorting are authorized on any column of your model