Improve joined model update/delete. (#71)

* Improve exception catching in Persistence_SQL

* Use single-table update and single-table delete with where id=X

$m->save() invokes update with a fixed ID. Also it updates joined
tables separately. Because the record has been loaded successfully
before and will be reloaded after updates (in some cases) at a risk of
failed transaction, we don't have to invoke action here.

Action is more suited for all-set update and if you use joins with
SQLite you're on your own, as it does not support join with update.

Same goes for deletion.

* Remove commented out code.

* Expanded documentation.

docs/advanced.rst

@@ -275,4 +275,52 @@ You can still access the deleted records::
 
 Calling delete() on the model with 'deleted_only' property will delete it permanently.
 
+Creating Unique Field
+=====================
+
+Database can has UNIQUE constraint, but this does work if you use DataSet. For instance, you
+may be only able to create one 'Category'  with name 'Book', but what if there is a
+soft-deleted record with same name or record that belongs to another user?
+
+With Agile Data you can create controller that will ensure that certain fields inside
+your model are unique::
+
+    class Controller_UniqueFields {
+        use \atk4\core\InitializerTrait {
+            init as _init;
+        }
+        use \atk4\core\TrackableTrait;
+
+        protected $fields = null;
+
+        function init() {
+            $this->_init();
+
+            // by default make 'name' unique
+            if (!$this->fields) {
+                $this->fields = [$this->owner->title_field];
+            }
+
+            $this->owner->addHook('beforeSave', $this);
+        }
+
+        function beforeSave($m) 
+        {
+            foreach ($this->fields as $field) {
+                if ($m->dirty[$field]) {
+                    $mm = clone $m;
+                    $mm->addCondition($mm->id_field != $this->id);
+                    $mm->tryLoadBy($field, $m[$field]);
+
+                    if ($mm->loaded()) {
+                        throw new \atk4\core\Exception(['Duplicate record exists', 'field'=>$field, 'value'=>$m[$field]]);
+                    }
+                }
+            }
+        }
+    }
+
+As expected - when you add a new model the new values are checked against existing records. You can also slightly modify the logic
+to make addCondition additive if you are verifying for the combination of matched fields.
+
 

src/Join_SQL.php

@@ -194,11 +194,9 @@ public function beforeUpdateQuery($model, $query)
             return;
         }
 
-        //if ($this->dsql->args['set']) {
         $update = $this->dsql();
         $update->where($this->foreign_field, $this->id);
         $update->update();
-        //}
     }
 
     public function doDelete($model, $id)
@@ -211,13 +209,7 @@ public function doDelete($model, $id)
         $delete
             ->where($this->foreign_field, $this->id);
 
-        //if ($this->delete_behaivour == 'cascade') {
-            $delete->delete()->execute();
-        //} elseif ($this->delete_behaivour == 'setnull') {
-            //$delete
-                //->set($this->foreign_field, null)
-                //->update();
-        //}
+        $delete->delete()->execute();
     }
 
     public function set($field, $value)

src/Persistence_SQL.php

@@ -419,7 +419,7 @@ public function load(Model $m, $id)
         // execute action
         try {
             $data = $load->getRow();
-        } catch (\Exception $e) {
+        } catch (\PDOException $e) {
             throw new Exception([
                 'Unable to load due to query error',
                 'query'      => $load->getDebugQuery(false),
@@ -505,7 +505,7 @@ public function loadAny(Model $m)
 
         if (!$data) {
             throw new Exception([
-                'Unable to load record',
+                'Unable to load any record',
                 'model' => $m,
                 'query' => $load->getDebugQuery(false),
             ]);
@@ -581,7 +581,7 @@ public function insert(Model $m, $data)
         try {
             $m->hook('beforeInsertQuery', [$insert]);
             $st = $insert->execute();
-        } catch (\Exception $e) {
+        } catch (\PDOException $e) {
             throw new Exception([
                 'Unable to execute insert query',
                 'query'      => $insert->getDebugQuery(false),
@@ -623,7 +623,7 @@ public function prepareIterator(Model $m)
             $export = $this->action($m, 'select');
 
             return $export->execute();
-        } catch (\Exception $e) {
+        } catch (\PDOException $e) {
             throw new Exception([
                 'Unable to execute iteration query',
                 'query'      => $export->getDebugQuery(false),
@@ -642,7 +642,8 @@ public function prepareIterator(Model $m)
      */
     public function update(Model $m, $id, $data)
     {
-        $update = $this->action($m, 'update');
+        $update = $this->initQuery($m);
+        $update->mode('update');
 
         // only apply fields that has been modified
         $cnt = 0;
@@ -662,7 +663,7 @@ public function update(Model $m, $id, $data)
         try {
             $m->hook('beforeUpdateQuery', [$update]);
             $st = $update->execute();
-        } catch (\Exception $e) {
+        } catch (\PDOException $e) {
             throw new Exception([
                 'Unable to update due to query error',
                 'query'      => $update->getDebugQuery(false),
@@ -687,16 +688,16 @@ public function update(Model $m, $id, $data)
      */
     public function delete(Model $m, $id)
     {
-        $delete = $this->action($m, 'delete');
-        $delete->reset('where'); // because it could have join there..
+        $delete = $this->initQuery($m);
+        $delete->mode('delete');
         $delete->where($m->id_field, $id);
         $m->hook('beforeDeleteQuery', [$delete]);
 
         try {
             $delete->execute();
-        } catch (\Exception $e) {
+        } catch (\PDOException $e) {
             throw new Exception([
-                'Unable to load due to query error',
+                'Unable to delete due to query error',
                 'query'      => $delete->getDebugQuery(false),
                 'model'      => $m,
                 'conditions' => $m->conditions,