Getting errors frequently in magento2

Question

I migrated the database of magento 1.9.x website to magento 2 using the data-migration-tool. After migrating the database the products and categories are displayed at the backend. Now when I cleared my cache am getting an error like

There has been an error processing your request Exception printing is disabled by default for security reasons. Error log record number: 1863159107

in both frontend and backend. This error is happening for even a small change made at backend or frontend(clearing cache, redindexing) and when I run the command php magento setup:static-content:deploy Its getting error like more than one default website is defined. Someone please help me regarding this issue. The error in 1863159107 is

 a:4:{i:0;s:40:"More than one default website is defined";i:1;s:2115:"#0   C:\xampp\htdocs\mage2.0.4\vendor\magento\module- store\Model\StoreResolver\Website.php(46):  Magento\Store\Model\WebsiteRepository->getDefault()
#1 C:\xampp\htdocs\mage2.0.4\vendor\magento\module-store\Model\StoreResolver.php(130): Magento\Store\Model\StoreResolver\Website->getAllowedStoreIds(NULL)
#2 C:\xampp\htdocs\mage2.0.4\vendor\magento\module-store\Model\StoreResolver.php(116): Magento\Store\Model\StoreResolver->readStoresData()
#3 C:\xampp\htdocs\mage2.0.4\vendor\magento\module-store\Model\StoreResolver.php(85): Magento\Store\Model\StoreResolver->getStoresData()
#4 C:\xampp\htdocs\mage2.0.4\vendor\magento\module-store\Model\StoreManager.php(151): Magento\Store\Model\StoreResolver->getCurrentStoreId()
#5 C:\xampp\htdocs\mage2.0.4\vendor\magento\module-store\App\Request\PathInfoProcessor.php(39): Magento\Store\Model\StoreManager->getStore('')
#6 C:\xampp\htdocs\mage2.0.4\vendor\magento\module-backend\App\Request\PathInfoProcessor.php(47): Magento\Store\App\Request\PathInfoProcessor->process(Object(Magento\Framework\App\Request\Http), '/')
#7 C:\xampp\htdocs\mage2.0.4\var\generation\Magento\Backend\App\Request\PathInfoProcessor\Proxy.php(95): Magento\Backend\App\Request\PathInfoProcessor->process(Object(Magento\Framework\App\Request\Http), '/')
#8 C:\xampp\htdocs\mage2.0.4\vendor\magento\framework\App\Request\Http.php(161): Magento\Backend\App\Request\PathInfoProcessor\Proxy->process(Object(Magento\Framework\App\Request\Http), '/')
#9 C:\xampp\htdocs\mage2.0.4\vendor\magento\framework\HTTP\PhpEnvironment\Request.php(194): Magento\Framework\App\Request\Http->setPathInfo()
#10 C:\xampp\htdocs\mage2.0.4\vendor\magento\framework\App\Request\Http.php(204): Magento\Framework\HTTP\PhpEnvironment\Request->getPathInfo()
#11 C:\xampp\htdocs\mage2.0.4\vendor\magento\framework\App\Http.php(110): Magento\Framework\App\Request\Http->getFrontName()
#12 C:\xampp\htdocs\mage2.0.4\vendor\magento\framework\App\Bootstrap.php(258): Magento\Framework\App\Http->launch()
#13 C:\xampp\htdocs\mage2.0.4\index.php(39): Magento\Framework\App\Bootstrap->run(Object(Magento\Framework\App\Http))
#14 {main}";s:3:"url";s:11:"/mage2.0.4/";s:11:"script_name";s:20:"/mage2.0.4/index.php";}

Not only this issue, In magento 2 when I try to change some style in frontend,the styles are getting lost and page is displayed like below

why is this happening?

Answer 1

I ran into this same error on a multi-website project and it seems if you change the default website's name to anything other than Main Website, Magento creates a new store record, but keeps the old one!

The exception is thrown in this file ./vendor/magento/module-store/Model/WebsiteRepository.php

private function initDefaultWebsite()
{
    $websites = (array) $this->getAppConfig()->get('scopes', 'websites', []);
    foreach ($websites as $data) {
        if (isset($data['is_default']) && $data['is_default'] == 1) {
            if ($this->default) {
                throw new \DomainException(__('More than one default website is defined'));
            }
    // ...

Dumping out the contents of $websites I found

Array
(
    [admin] => Array
        (
            [website_id] => 0
            [code] => admin
            [name] => Admin
            [sort_order] => 0
            [default_group_id] => 0
            [is_default] => 0
        )

    [base] => Array
        (
            [website_id] => 1
            [code] => base
            [name] => Main Website
            [sort_order] => 0
            [default_group_id] => 1
            [is_default] => 1
        )

    [wholesale] => Array
        (
            [website_id] => 2
            [code] => wholesale
            [name] => Wholesale
            [sort_order] => 2
            [default_group_id] => 2
            [is_default] => 0
        )

    [retail] => Array
        (
            [website_id] => 1
            [code] => retail
            [name] => Retail
            [sort_order] => 0
            [default_group_id] => 1
            [is_default] => 1
        )

)

Notice, base and retail both have is_default set... Changing the name of the default website back to Main Website seems to have fixed the problem as the last record went away when doing so.

In conclusion, the Main Website is magical and should not be renamed from what I can tell.