abdullah/til
1
0
Fork 0
mirror of https://github.com/jbranchaud/til synced 2026-01-03 15:18:01 +00:00
Code Issues Projects Releases Wiki Activity

Add Perform SQL Explain With ActiveRecord as a rails til

Browse Source
This commit is contained in:
jbranchaud
2016-05-01 17:15:44 -05:00
parent cac58b4248
commit 3cb656fe99
2 changed files with 26 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
README.md
View File

@@ -7,7 +7,7 @@ variety of languages and technologies. These are things that don't really
warrant a full blog post. These are mostly things I learn by pairing with
smart people at [Hashrocket](http://hashrocket.com/).
_407 TILs and counting..._
_408 TILs and counting..._
---
@@ -268,6 +268,7 @@ _407 TILs and counting..._
- [Ignore Poltergeist JavaScript Errors](rails/ignore-poltergeist-javascript-errors.md)
- [Migrating Up Down Up](rails/migrating-up-down-up.md)
- [Params Includes Submission Button Info](rails/params-includes-submission-button-info.md)
- [Perform SQL Explain With ActiveRecord](rails/perform-sql-explain-with-activerecord.md)
- [Pretend Generations](rails/pretend-generations.md)
- [Rescue From](rails/rescue-from.md)
- [Retrieve An Object If It Exists](rails/retrieve-an-object-if-it-exists.md)

24
rails/perform-sql-explain-with-activerecord.md Normal file
View File

@@ -0,0 +1,24 @@
# Perform SQL Explain With ActiveRecord
Want to check out the performance characteristics of some SQL query from
within a Pry session? `ActiveRecord` allows you to perform a SQL `explain`
on any `ActiveRecord::Relation` object. After chaining some Arel functions
together, add an `#explain`.
Here is an example:
```ruby
Recipe.all.joins(:ingredient_amounts).explain
Recipe Load (0.9ms) SELECT "recipes".* FROM "recipes" INNER JOIN "ingredient_amounts" ON "ingredient_amounts"."recipe_id" = "recipes"."id"
=> EXPLAIN for: SELECT "recipes".* FROM "recipes" INNER JOIN "ingredient_amounts" ON "ingredient_amounts"."recipe_id" = "recipes"."id"
QUERY PLAN
----------------------------------------------------------------------------
Hash Join (cost=1.09..26.43 rows=22 width=148)
Hash Cond: (ingredient_amounts.recipe_id = recipes.id)
-> Seq Scan on ingredient_amounts (cost=0.00..21.00 rows=1100 width=4)
-> Hash (cost=1.04..1.04 rows=4 width=148)
-> Seq Scan on recipes (cost=0.00..1.04 rows=4 width=148)
(5 rows)
```
[source](https://robots.thoughtbot.com/why-postgres-wont-always-use-an-index)