Controller.php

$_vendorModel = $this->instantiate('Vendor')->find()->where(['name' => $vendorModel->name])->one();
if (is_null($_vendorModel)) {
    $_vendorModel       = $this->instantiate('Vendor');
    $_vendorModel->name = $vendorModel->name;
    $success            = $_vendorModel->save();

    $dirtyAttributes = $itemVendorModel->dirtyAttributes;
    $dirtyAttributes = array_filter($dirtyAttributes, function($v) { return $v !== ""; });

    if (! $success
        && count($dirtyAttributes) > 0
    ) {
        $message = "Item {$model->name} saved without vendor attributes because of errors with vendor attributes";
        if (isset($warnings[$lineNum])) {
            $warnings[$lineNum] = [$warnings[$lineNum], $message];
        } else {
            $warnings[$lineNum] = $message;
        }
    }

    $vendorModel = $_vendorModel;
}

// This generates the following queries
/*
SELECT * FROM `vendor` WHERE `name`='' ORDER BY `name`
SELECT * FROM `vendor_contact` WHERE `vendor_id`='6f546ed5-76c3-4bc7-9531-c869bcc5337b'
SELECT * FROM `contact` WHERE (`status`='1') AND (0=1)
SELECT * FROM `vendor_address` WHERE `vendor_id`='6f546ed5-76c3-4bc7-9531-c869bcc5337b'
SELECT * FROM `address` WHERE (`status`='1') AND (0=1)
SELECT COUNT(*) FROM `vendor` WHERE `id`='6f546ed5-76c3-4bc7-9531-c869bcc5337b' ORDER BY `name`
*/

// 6f546ed5-76c3-4bc7-9531-c869bcc5337b is not a UUID used anywhere in my database

Vendor.php

 public function rules()
    {
        return [
            ['id', 'default', 'value' => Uuid::generate()],
            [['name'], 'required'],
            [['created_at', 'updated_at', 'code', 'website', 'duns', 'terms_id', 'created_by', 'updated_at', 'created_at',
                'contacts', 'address', 'updated_by'], 'safe'],
            [['name'], 'string', 'max' => 64],
            [['name'], 'unique'],
            ['status', 'default', 'value' => 1],
            [['fax_number', 'account_number', 'quickbooks_list_id'], 'string'],
            [['quickbooks_last_sync'], 'number']

        ];
    }

    public function fields()
    {
        return array_merge(parent::fields(), ['contacts', 'attachments', 'notes', 'address']);
    }

public function getContacts()
    {
        return $this->hasMany(Contact::className(), ['id' => 'contact_id'])
            ->viaTable('{{%vendor_contact}}', ['vendor_id' => 'id']);

    }
public function getAddress()
    {
       return $this->hasOne(Address::className(), ['id' => 'address_id'])
            ->viaTable('{{%vendor_address}}', ['vendor_id' => 'id']);
    }

public function actionMytest()
{
    Yii::trace('1');
    Vendor::find()->where(['name' => 'somgthing'])->one();
    Yii::trace('2');
}