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author | Rafael França <rafaelmfranca@gmail.com> | 2017-11-14 13:59:00 -0500 |
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committer | GitHub <noreply@github.com> | 2017-11-14 13:59:00 -0500 |
commit | b9675aa72252671c167721b597071e5751b1d409 (patch) | |
tree | f32ea1725a0a3d82afd79c0ec9bc76962e2e0b32 /README.md | |
parent | b0ad8046091ce45a20fc7a5cb68b4599f876bbbb (diff) | |
parent | 27a7af81bd274f8036f42638acdb47e85e76c5aa (diff) | |
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Merge pull request #501 from abelards/patch-1
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-rw-r--r-- | README.md | 5 |
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@@ -188,7 +188,7 @@ users.project(users[:age].average.as("mean_age")) # => SELECT AVG(users.age) AS mean_age FROM users ``` -### The Crazy Features +### The Advanced 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). @@ -215,6 +215,7 @@ products. #### Complex Joins +##### Alias Where Arel really shines is in its ability to handle complex joins and aggregations. As a first example, let's consider an "adjacency list", a tree represented in a table. Suppose we have a table `comments`, representing a threaded discussion: ```ruby @@ -240,6 +241,7 @@ comments_with_replies = \ This will return the reply for the first comment. +##### CTE [Common Table Expressions (CTE)](https://en.wikipedia.org/wiki/Common_table_expressions#Common_table_expression) support via: Create a `CTE` @@ -262,6 +264,7 @@ users. # FROM users INNER JOIN cte_table ON users.id = cte_table.user_id ``` +#### Write SQL strings When your query is too complex for `Arel`, you can use `Arel::SqlLiteral`: ```ruby |