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Diffstat (limited to 'README.md')
| -rw-r--r-- | README.md | 13 |
1 files changed, 11 insertions, 2 deletions
@@ -150,7 +150,13 @@ The `OR` operator works like this: users.where(users[:name].eq('bob').or(users[:age].lt(25))) ``` -The `AND` operator behaves similarly. Here is an example of the `DISTINCT` operator: +The `AND` operator behaves similarly (same exact behaviour as chained calls to `.where`): + +```ruby +users.where(users[:name].eq('bob').and(users[:age].lt(25))) +``` + +Here is an example of the `DISTINCT` operator: ```ruby posts = Arel::Table.new(:posts) @@ -188,7 +194,7 @@ 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 +221,7 @@ 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 +247,7 @@ 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 +270,7 @@ 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 |