#715108: implementation of MergeQuery specific to SQLite.

From: Damien Tournoud <damz@dzdev.local>


---
 database/sqlite/query.inc |   64 ++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 63 insertions(+), 1 deletions(-)

diff --git includes/database/sqlite/query.inc includes/database/sqlite/query.inc
index 8be26c1..f9714f2 100644
--- includes/database/sqlite/query.inc
+++ includes/database/sqlite/query.inc
@@ -63,7 +63,6 @@ class InsertQuery_sqlite extends InsertQuery {
  *   UPDATE test SET name = 'newname' WHERE tid = 1 AND name <> 'newname'
  */
 class UpdateQuery_sqlite extends UpdateQuery {
-
   /**
    * Helper function that removes the fields that are already in a condition.
    *
@@ -84,6 +83,10 @@ class UpdateQuery_sqlite extends UpdateQuery {
   }
 
   public function execute() {
+    if (!empty($this->queryOptions['sqlite_return_matched_rows'])) {
+      return parent::execute();
+    }
+
     // Get the fields used in the update query, and remove those that are already
     // in the condition.
     $fields = $this->expressionFields + $this->fields;
@@ -116,6 +119,65 @@ class UpdateQuery_sqlite extends UpdateQuery {
 }
 
 /**
+ * SQLite specific implementation of MergeQuery.
+ *
+ * SQLite doesn't support row-level locking, but acquire locks on the whole
+ * database file. We implement MergeQuery using a different strategy:
+ *   - UPDATE xxx WHERE <key condition>
+ *   - if the previous query hasn't matched, INSERT
+ *
+ * The first UPDATE query will acquire a RESERVED lock on the database.
+ */
+class MergeQuery_sqlite extends MergeQuery {
+  public function execute() {
+    // If validation fails, simply return NULL.
+    // Note that validation routines in preExecute() may throw exceptions instead.
+    if (!$this->preExecute()) {
+      return NULL;
+    }
+
+    // Wrap multiple queries in a transaction.
+    $transaction = $this->connection->startTransaction();
+
+    if ($this->updateFields) {
+      $update_fields = $this->updateFields;
+    }
+    else {
+      $update_fields = $this->insertFields;
+      // If there are no exclude fields, this is a no-op.
+      foreach ($this->excludeFields as $exclude_field) {
+        unset($update_fields[$exclude_field]);
+      }
+    }
+
+    // The update fields are empty, fill them with dummy data.
+    if (!$update_fields && !$this->expressionFields) {
+      $update_fields = array_slice($this->keyFields, 0, 1);
+    }
+
+    // Start with an update query, this acquires a RESERVED lock on the database.
+    // Use the SQLite-specific 'sqlite_return_matched_rows' query option to
+    // return the number of rows matched by that query, not modified by it.
+    $update = $this->connection->update($this->table, array('sqlite_return_matched_rows' => TRUE) + $this->queryOptions)->fields($update_fields);
+
+    foreach ($this->keyFields as $field => $value) {
+      $update->condition($field, $value);
+    }
+    foreach ($this->expressionFields as $field => $expression) {
+      $update->expression($field, $expression['expression'], $expression['arguments']);
+    }
+    if ($update->execute()) {
+      return MergeQuery::STATUS_UPDATE;
+    }
+
+    // The UPDATE query failed to match rows, proceed with an INSERT.
+    $insert_fields = $this->insertFields + $this->keyFields;
+    $this->connection->insert($this->table, $this->queryOptions)->fields($insert_fields)->execute();
+    return MergeQuery::STATUS_INSERT;
+  }
+}
+
+/**
  * SQLite specific implementation of DeleteQuery.
  *
  * When the WHERE is omitted from a DELETE statement and the table being deleted