131 lines
4.9 KiB
Plaintext
131 lines
4.9 KiB
Plaintext
= Aggregate Column Behavior =
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The `aggregate_column` behavior keeps a column updated using an aggregate function executed on a related table.
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== Basic Usage ==
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In the `schema.xml`, use the `<behavior>` tag to add the `aggregate_column` behavior to a table. You must provide parameters for the aggregate column `name`, the foreign table name, and the aggegate `expression`. For instance, to add an aggregate column keeping the comment count in a `post` table:
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{{{
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#!xml
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<table name="post">
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<column name="id" type="INTEGER" required="true" primaryKey="true" autoIncrement="true" />
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<column name="title" type="VARCHAR" required="true" primaryString="true" />
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<behavior name="aggregate_column">
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<parameter name="name" value="nb_comments" />
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<parameter name="foreign_table" value="comment" />
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<parameter name="expression" value="COUNT(id)" />
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</behavior>
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</table>
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<table name="comment">
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<column name="id" type="INTEGER" required="true" primaryKey="true" autoIncrement="true" />
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<column name="post_id" type="INTEGER" />
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<foreign-key foreignTable="post" onDelete="cascade">
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<reference local="post_id" foreign="id" />
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</foreign-key>
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</table>
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}}}
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Rebuild your model, and insert the table creation sql again. The model now has an additional `nb_comments` column, of type `integer` by default. And each time an record from the foreign table is added, modified, or removed, the aggregate column is updated:
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{{{
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#!php
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<?php
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$post = new Post();
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$post->setTitle('How Is Life On Earth?');
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$post->save();
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echo $post->getNbComments(); // 0
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$comment1 = new Comment();
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$comment1->setPost($post);
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$comment1->save();
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echo $post->getNbComments(); // 1
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$comment2 = new Comment();
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$comment2->setPost($post);
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$comment2->save();
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echo $post->getNbComments(); // 2
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$comment2->delete();
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echo $post->getNbComments(); // 1
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}}}
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The aggregate column is also kept up to date when related records get modified through a Query object:
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{{{
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#!php
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<?php
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CommentQuery::create()
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->filterByPost($post)
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->delete():
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echo $post->getNbComments(); // 0
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}}}
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== Customizing The Aggregate Calculation ==
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Any aggregate function can be used on any of the foreign columns. For instance, you can use the `aggregate_column` behavior to keep the latest update date of the related comments, or the total votes on the comments. You can even keep several aggregate columns in a single table:
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{{{
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#!xml
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<table name="post">
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<column name="id" type="INTEGER" required="true" primaryKey="true" autoIncrement="true" />
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<column name="title" type="VARCHAR" required="true" primaryString="true" />
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<behavior name="aggregate_column">
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<parameter name="name" value="nb_comments" />
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<parameter name="foreign_table" value="comment" />
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<parameter name="expression" value="COUNT(id)" />
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</behavior>
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<behavior name="aggregate_column">
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<parameter name="name" value="last_comment" />
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<parameter name="foreign_table" value="comment" />
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<parameter name="expression" value="MAX(created_at)" />
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</behavior>
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<behavior name="aggregate_column">
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<parameter name="name" value="total_votes" />
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<parameter name="foreign_table" value="comment" />
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<parameter name="expression" value="SUM(vote)" />
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</behavior>
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</table>
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<table name="comment">
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<column name="id" type="INTEGER" required="true" primaryKey="true" autoIncrement="true" />
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<column name="post_id" type="INTEGER" />
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<foreign-key foreignTable="post" onDelete="cascade">
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<reference local="post_id" foreign="id" />
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</foreign-key>
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<column name="created_at" type="TIMESTAMP" />
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<column name="vote" type="INTEGER" />
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</table>
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}}}
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The behavior adds a `computeXXX()` method to the `Post` class to compute the value of the aggregate function. This method, called each time records are modified in the related `comment` table, is the translation of the behavior settings into a SQL query:
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{{{
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#!php
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<?php
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// in om/BasePost.php
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public function computeNbComments(PropelPDO $con)
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{
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$stmt = $con->prepare('SELECT COUNT(id) FROM `comment` WHERE comment.POST_ID = :p1');
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$stmt->bindValue(':p1', $this->getId());
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$stmt->execute();
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return $stmt->fetchColumn();
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}
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}}}
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You can override this method in the model class to customize the aggregate column calculation.
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== Customizing The Aggregate Column ==
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By default, the behavior adds one columns to the model. If this column is already described in the schema, the behavior detects it and doesn't add it a second time. This can be useful if you need to use a custom `type` or `phpName` for the aggregate column:
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{{{
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#!xml
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<table name="post">
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<column name="id" type="INTEGER" required="true" primaryKey="true" autoIncrement="true" />
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<column name="title" type="VARCHAR" required="true" primaryString="true" />
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<column name="nb_comments" phpName="CommentCount" type="INTEGER" />
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<behavior name="aggregate_column">
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<parameter name="name" value="nb_comments" />
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<parameter name="foreign_table" value="comment" />
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<parameter name="expression" value="COUNT(id)" />
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</behavior>
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</table>
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}}}
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