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-rw-r--r-- | README.md | 110 |
1 files changed, 75 insertions, 35 deletions
@@ -8,8 +8,8 @@ Arel Really Exasperates Logicians Arel is a SQL AST manager for Ruby. It -1. Simplifies the generation of complex SQL queries -2. Adapts to various RDBMSes +1. simplifies the generation of complex SQL queries, and +2. adapts to various RDBMSes. It is intended to be a framework framework; that is, you can build your own ORM with it, focusing on innovative object and collection modeling as opposed to @@ -17,7 +17,7 @@ database compatibility and query generation. ## Status -For the moment, Arel uses Active Record's connection adapters to connect to the various engines, connection pooling, perform quoting, and do type conversion. +For the moment, Arel uses Active Record's connection adapters to connect to the various engines and perform connection pooling, quoting, and type conversion. ## A Gentle Introduction @@ -27,7 +27,7 @@ Generating a query with Arel is simple. For example, in order to produce SELECT * FROM users ``` -you construct a table relation and convert it to sql: +you construct a table relation and convert it to SQL: ```ruby users = Arel::Table.new(:users) @@ -56,24 +56,48 @@ users.project(users[:id]) Comparison operators `=`, `!=`, `<`, `>`, `<=`, `>=`, `IN`: ```ruby -users.where(users[:age].eq(10)).project(Arel.sql('*')) # => SELECT * FROM "users" WHERE "users"."age" = 10 -users.where(users[:age].not_eq(10)).project(Arel.sql('*')) # => SELECT * FROM "users" WHERE "users"."age" != 10 -users.where(users[:age].lt(10)).project(Arel.sql('*')) # => SELECT * FROM "users" WHERE "users"."age" < 10 -users.where(users[:age].gt(10)).project(Arel.sql('*')) # => SELECT * FROM "users" WHERE "users"."age" > 10 -users.where(users[:age].lteq(10)).project(Arel.sql('*')) # => SELECT * FROM "users" WHERE "users"."age" <= 10 -users.where(users[:age].gteq(10)).project(Arel.sql('*')) # => SELECT * FROM "users" WHERE "users"."age" >= 10 -users.where(users[:age].in([20, 16, 17])).project(Arel.sql('*')) # => SELECT * FROM "users" WHERE "users"."age" IN (20, 16, 17) +users.where(users[:age].eq(10)).project(Arel.sql('*')) +# => SELECT * FROM "users" WHERE "users"."age" = 10 + +users.where(users[:age].not_eq(10)).project(Arel.sql('*')) +# => SELECT * FROM "users" WHERE "users"."age" != 10 + +users.where(users[:age].lt(10)).project(Arel.sql('*')) +# => SELECT * FROM "users" WHERE "users"."age" < 10 + +users.where(users[:age].gt(10)).project(Arel.sql('*')) +# => SELECT * FROM "users" WHERE "users"."age" > 10 + +users.where(users[:age].lteq(10)).project(Arel.sql('*')) +# => SELECT * FROM "users" WHERE "users"."age" <= 10 + +users.where(users[:age].gteq(10)).project(Arel.sql('*')) +# => SELECT * FROM "users" WHERE "users"."age" >= 10 + +users.where(users[:age].in([20, 16, 17])).project(Arel.sql('*')) +# => SELECT * FROM "users" WHERE "users"."age" IN (20, 16, 17) ``` Bitwise operators `&`, `|`, `^`, `<<`, `>>`: ```ruby -users.where((users[:bitmap] & 16).gt(0)).project(Arel.sql('*')) # => SELECT * FROM "users" WHERE ("users"."bitmap" & 16) > 0 -users.where((users[:bitmap] | 16).gt(0)).project(Arel.sql('*')) # => SELECT * FROM "users" WHERE ("users"."bitmap" | 16) > 0 -users.where((users[:bitmap] ^ 16).gt(0)).project(Arel.sql('*')) # => SELECT * FROM "users" WHERE ("users"."bitmap" ^ 16) > 0 -users.where((users[:bitmap] << 1).gt(0)).project(Arel.sql('*')) # => SELECT * FROM "users" WHERE ("users"."bitmap" << 1) > 0 -users.where((users[:bitmap] >> 1).gt(0)).project(Arel.sql('*')) # => SELECT * FROM "users" WHERE ("users"."bitmap" >> 1) > 0 -users.where((~ users[:bitmap]).gt(0)).project(Arel.sql('*')) # => SELECT FROM "users" WHERE ~ "users"."bitmap" > 0 +users.where((users[:bitmap] & 16).gt(0)).project(Arel.sql('*')) +# => SELECT * FROM "users" WHERE ("users"."bitmap" & 16) > 0 + +users.where((users[:bitmap] | 16).gt(0)).project(Arel.sql('*')) +# => SELECT * FROM "users" WHERE ("users"."bitmap" | 16) > 0 + +users.where((users[:bitmap] ^ 16).gt(0)).project(Arel.sql('*')) +# => SELECT * FROM "users" WHERE ("users"."bitmap" ^ 16) > 0 + +users.where((users[:bitmap] << 1).gt(0)).project(Arel.sql('*')) +# => SELECT * FROM "users" WHERE ("users"."bitmap" << 1) > 0 + +users.where((users[:bitmap] >> 1).gt(0)).project(Arel.sql('*')) +# => SELECT * FROM "users" WHERE ("users"."bitmap" >> 1) > 0 + +users.where((~ users[:bitmap]).gt(0)).project(Arel.sql('*')) +# => SELECT FROM "users" WHERE ~ "users"."bitmap" > 0 ``` Joins resemble SQL strongly: @@ -83,7 +107,7 @@ users.join(photos).on(users[:id].eq(photos[:user_id])) # => SELECT * FROM users INNER JOIN photos ON users.id = photos.user_id ``` -Left Joins +Left joins: ```ruby users.join(photos, Arel::Nodes::OuterJoin).on(users[:id].eq(photos[:user_id])) @@ -104,7 +128,7 @@ users.project(users[:name]).group(users[:name]) # => SELECT users.name FROM users GROUP BY users.name ``` -The best property of arel is its "composability", or closure under all operations. For example, to restrict AND project, just "chain" the method invocations: +The best property of Arel is its "composability," or closure under all operations. For example, to restrict AND project, just "chain" the method invocations: ```ruby users \ @@ -130,23 +154,35 @@ The `AND` operator behaves similarly. Aggregate functions `AVG`, `SUM`, `COUNT`, `MIN`, `MAX`, `HAVING`: ```ruby -photos.group(photos[:user_id]).having(photos[:id].count.gt(5)) # => SELECT FROM photos GROUP BY photos.user_id HAVING COUNT(photos.id) > 5 -users.project(users[:age].sum) # => SELECT SUM(users.age) FROM users -users.project(users[:age].average) # => SELECT AVG(users.age) FROM users -users.project(users[:age].maximum) # => SELECT MAX(users.age) FROM users -users.project(users[:age].minimum) # => SELECT MIN(users.age) FROM users -users.project(users[:age].count) # => SELECT COUNT(users.age) FROM users +photos.group(photos[:user_id]).having(photos[:id].count.gt(5)) +# => SELECT FROM photos GROUP BY photos.user_id HAVING COUNT(photos.id) > 5 + +users.project(users[:age].sum) +# => SELECT SUM(users.age) FROM users + +users.project(users[:age].average) +# => SELECT AVG(users.age) FROM users + +users.project(users[:age].maximum) +# => SELECT MAX(users.age) FROM users + +users.project(users[:age].minimum) +# => SELECT MIN(users.age) FROM users + +users.project(users[:age].count) +# => SELECT COUNT(users.age) FROM users ``` Aliasing Aggregate Functions: ```ruby -users.project(users[:age].average.as("mean_age")) # => SELECT AVG(users.age) AS mean_age FROM users +users.project(users[:age].average.as("mean_age")) +# => SELECT AVG(users.age) AS mean_age FROM users ``` ### The Crazy Features -The examples above are fairly simple and other libraries match or come close to matching the expressiveness of Arel (e.g., `Sequel` in Ruby). +The examples above are fairly simple and other libraries match or come close to matching the expressiveness of Arel (e.g. `Sequel` in Ruby). #### Inline math operations @@ -190,12 +226,13 @@ Joining a table to itself requires aliasing in SQL. This aliasing can be handled replies = comments.alias comments_with_replies = \ comments.join(replies).on(replies[:parent_id].eq(comments[:id])).where(comments[:id].eq(1)) -# => SELECT * FROM comments INNER JOIN comments AS comments_2 WHERE comments_2.parent_id = comments.id AND comments.id = 1 +# => SELECT * FROM comments INNER JOIN comments AS comments_2 +# WHERE comments_2.parent_id = comments.id AND comments.id = 1 ``` This will return the reply for the first comment. -[Common Table Expressions(CTE)](https://en.wikipedia.org/wiki/Common_table_expressions#Common_table_expression) support via: +[Common Table Expressions (CTE)](https://en.wikipedia.org/wiki/Common_table_expressions#Common_table_expression) support via: Create a `CTE` @@ -212,7 +249,9 @@ users. project(users[:id], cte_table[:click].sum). with(composed_cte) -# => WITH cte_table AS (SELECT FROM photos WHERE photos.created_at > '2014-05-02') SELECT users.id, SUM(cte_table.click) FROM users INNER JOIN cte_table ON users.id = cte_table.user_id +# => WITH cte_table AS (SELECT FROM photos WHERE photos.created_at > '2014-05-02') +# SELECT users.id, SUM(cte_table.click) +# FROM users INNER JOIN cte_table ON users.id = cte_table.user_id ``` When your query is too complex for `Arel`, you can use `Arel::SqlLiteral`: @@ -225,17 +264,18 @@ photo_clicks = Arel::Nodes::SqlLiteral.new(<<-SQL ELSE default_calculation END SQL ) + photos.project(photo_clicks.as("photo_clicks")) # => SELECT CASE WHEN condition1 THEN calculation1 - WHEN condition2 THEN calculation2 - WHEN condition3 THEN calculation3 - ELSE default_calculation END - FROM "photos" +# WHEN condition2 THEN calculation2 +# WHEN condition3 THEN calculation3 +# ELSE default_calculation END +# FROM "photos" ``` ## Contributing to Arel -Arel is work of many contributors. You're encouraged to submit pull requests, propose +Arel is the work of many contributors. You're encouraged to submit pull requests, propose features and discuss issues. See [CONTRIBUTING](CONTRIBUTING.md). |