update symfony 2.8 to 3.* , sonata errors - php

Question

i would like update my symfony projet ( current 2.8 to sf 3.* )
this is my composer.json file ( requiere part )
"require": {
"php": ">=5.3.9",
"symfony/symfony": "2.8.*",
"doctrine/orm": "^2.4.8",
"doctrine/doctrine-bundle": "~1.4",
"symfony/assetic-bundle": "~2.3",
"symfony/swiftmailer-bundle": "~2.3",
"symfony/monolog-bundle": "~2.4",
"sensio/distribution-bundle": "~4.0",
"sensio/framework-extra-bundle": "^3.0.2",
"incenteev/composer-parameter-handler": "~2.0",
"sonata-project/media-bundle": "^2.3",
"sonata-project/user-bundle": "^2.2",
"sonata-project/formatter-bundle": "~2.3",
"sonata-project/doctrine-orm-admin-bundle": "~2.2",
"sonata-project/admin-bundle": "~2.2",
"sonata-project/timeline-bundle": "^2.2",
"sonata-project/intl-bundle": "^2.2",
"sonata-project/cache-bundle": "^2.2",
"liuggio/excelbundle": "^2.0",
"friendsofsymfony/elastica-bundle": "^3.1",
"liip/imagine-bundle": "^1.4",
"friendsofsymfony/jsrouting-bundle": "^1.6",
"gos/web-socket-bundle": "^1.8"
},
If i change
"symfony/symfony": "2.8.*",
to
"symfony/symfony": "~3.0",
and do
php composer.phar update symfony/symfony --with-dependencies
but i have this error
Problem 1
- sonata-project/media-bundle 2.3.4 requires symfony/symfony ~2.3 -> satisfiable by symfony/symfony
So i tried to update media-bundle to 3.10.1 but it give me an error in another sonata bundle ..
how should I do things right?
I have to update the modules one by one?
or update my composer.json with all modifications ?
thanks

Answer 1

Your sonata dependencies are very too old and does not support Symfony 3.
Sample: https://github.com/sonata-project/SonataMediaBundle/blob/2.x/composer.json
You must upgrade your dependencies to make it working.
Also, you can use the composer why-not command to get more help.

Answer 2

I also got stuck in this error a few times. The error message is kinda abstract.
To solve this error you need to update the version for sonata-project/media-bundle in your composer.json file.
So you can replace it with: "sonata-project/media-bundle": "^3.1",
Then run composer update command again. You might get the same error you got above but for another package. Update that as well. Repeat this until your composer update command is successful.
At that point, if you are lucky your application will work. If not you need to update the code to use the new package version code. Remember, updating the first number of a package (from 2.8 to 3.something) means that is a breaking compatibility update.
Later update: if you check the composer.json file of sonata-project/media-bundle version 2.3 here: https://github.com/sonata-project/SonataMediaBundle/blob/2.3.0/composer.json you will see that it requires symfony version: "symfony/symfony": "~2.3" and you want to update to symfony version 3.something. So they are incompatible. That's why you also need to update this package and so on. Composer will do this behind the scenes and throw that error when your packages or their dependencies are not compatible between them.
Hope that helps.