yii\gii\generators\model\Generator::generateRules PHP Method

    public function generateRules($table)
    {
        $types = [];
        $lengths = [];
        foreach ($table->columns as $column) {
            if ($column->autoIncrement) {
                continue;
            }
            if (!$column->allowNull && $column->defaultValue === null) {
                $types['required'][] = $column->name;
            }
            switch ($column->type) {
                case Schema::TYPE_SMALLINT:
                case Schema::TYPE_INTEGER:
                case Schema::TYPE_BIGINT:
                    $types['integer'][] = $column->name;
                    break;
                case Schema::TYPE_BOOLEAN:
                    $types['boolean'][] = $column->name;
                    break;
                case Schema::TYPE_FLOAT:
                case 'double':
                    // Schema::TYPE_DOUBLE, which is available since Yii 2.0.3
                // Schema::TYPE_DOUBLE, which is available since Yii 2.0.3
                case Schema::TYPE_DECIMAL:
                case Schema::TYPE_MONEY:
                    $types['number'][] = $column->name;
                    break;
                case Schema::TYPE_DATE:
                case Schema::TYPE_TIME:
                case Schema::TYPE_DATETIME:
                case Schema::TYPE_TIMESTAMP:
                    $types['safe'][] = $column->name;
                    break;
                default:
                    // strings
                    if ($column->size > 0) {
                        $lengths[$column->size][] = $column->name;
                    } else {
                        $types['string'][] = $column->name;
                    }
            }
        }
        $rules = [];
        foreach ($types as $type => $columns) {
            $rules[] = "[['" . implode("', '", $columns) . "'], '{$type}']";
        }
        foreach ($lengths as $length => $columns) {
            $rules[] = "[['" . implode("', '", $columns) . "'], 'string', 'max' => {$length}]";
        }
        $db = $this->getDbConnection();
        // Unique indexes rules
        try {
            $uniqueIndexes = $db->getSchema()->findUniqueIndexes($table);
            foreach ($uniqueIndexes as $uniqueColumns) {
                // Avoid validating auto incremental columns
                if (!$this->isColumnAutoIncremental($table, $uniqueColumns)) {
                    $attributesCount = count($uniqueColumns);
                    if ($attributesCount === 1) {
                        $rules[] = "[['" . $uniqueColumns[0] . "'], 'unique']";
                    } elseif ($attributesCount > 1) {
                        $labels = array_intersect_key($this->generateLabels($table), array_flip($uniqueColumns));
                        $lastLabel = array_pop($labels);
                        $columnsList = implode("', '", $uniqueColumns);
                        $rules[] = "[['{$columnsList}'], 'unique', 'targetAttribute' => ['{$columnsList}'], 'message' => 'The combination of " . implode(', ', $labels) . " and {$lastLabel} has already been taken.']";
                    }
                }
            }
        } catch (NotSupportedException $e) {
            // doesn't support unique indexes information...do nothing
        }
        // Exist rules for foreign keys
        foreach ($table->foreignKeys as $refs) {
            $refTable = $refs[0];
            $refTableSchema = $db->getTableSchema($refTable);
            if ($refTableSchema === null) {
                // Foreign key could point to non-existing table: https://github.com/yiisoft/yii2-gii/issues/34
                continue;
            }
            $refClassName = $this->generateClassName($refTable);
            unset($refs[0]);
            $attributes = implode("', '", array_keys($refs));
            $targetAttributes = [];
            foreach ($refs as $key => $value) {
                $targetAttributes[] = "'{$key}' => '{$value}'";
            }
            $targetAttributes = implode(', ', $targetAttributes);
            $rules[] = "[['{$attributes}'], 'exist', 'skipOnError' => true, 'targetClass' => {$refClassName}::className(), 'targetAttribute' => [{$targetAttributes}]]";
        }
        return $rules;
    }

 /**
  * @inheritdoc
  */
 public function generateRules($table)
 {
     $rules = parent::generateRules($table);
     if ($this->includeTimestampBehavior) {
         // Assume same datatype for created_at/updated_at columns
         $this->_useDatetimeValue = isset($table->columns[$this->createdColumnName]) && $table->columns[$this->createdColumnName]->type === Schema::TYPE_DATETIME;
         foreach ($rules as $i => $rule) {
             if (strpos($rule, "'{$this->createdColumnName}'") === false && strpos($rule, "'{$this->updatedColumnName}'") === false || strpos($rule, "'exist', " !== false)) {
                 continue;
             }
             list($ruleFields, $ruleName) = eval("return {$rule};");
             if (($key = array_search($this->createdColumnName, $ruleFields)) !== false) {
                 unset($ruleFields[$key]);
             }
             if (($key = array_search($this->updatedColumnName, $ruleFields)) !== false) {
                 unset($ruleFields[$key]);
             }
             if (empty($ruleFields)) {
                 unset($rules[$i]);
             } else {
                 $newRuleFields = "['" . implode("', '", $ruleFields) . "']";
                 $rules[$i] = preg_replace('#^\\[\\[[^\\]]+\\]#', '[' . $newRuleFields, $rule);
             }
         }
     }
     return $rules;
 }