之前说的，我一直是将macOS作为开发平台，直接在macOS系统配置Nginx PHP及MySQL，由于项目需求，需要使用到MongoDB，这篇就是一部在macOS系统下运行Laravel框架使用MongoDB遇到问题解决问题的流水账。
为了不污染正式开发的代码，我新建了一个Laravel工程，版本是5.5 LTS，MongoDB扩展使用的是laravel-mongodb，根据文档，安装该扩展的命令为：
composer require jenssegers/mongodb
但是一执行这条命令，就出现了一大堆的错误：
zocoMac:laravel-test zoco$ composer require jenssegers/mongodb
Using version ^3.4 for jenssegers/mongodb
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.
Problem 1
- jenssegers/mongodb v3.4.0 requires mongodb/mongodb ^1.0.0 -> satisfiable by mongodb/mongodb[1.0.0, 1.0.1, 1.0.2, 1.0.3, 1.0.4, 1.0.5, 1.1.0, 1.1.1, 1.1.2, 1.2.0, 1.3.0, 1.3.1, 1.3.2, 1.4.0, 1.4.1, 1.4.2].
- jenssegers/mongodb v3.4.1 requires mongodb/mongodb ^1.0.0 -> satisfiable by mongodb/mongodb[1.0.0, 1.0.1, 1.0.2, 1.0.3, 1.0.4, 1.0.5, 1.1.0, 1.1.1, 1.1.2, 1.2.0, 1.3.0, 1.3.1, 1.3.2, 1.4.0, 1.4.1, 1.4.2].
- jenssegers/mongodb v3.4.2 requires mongodb/mongodb ^1.0.0 -> satisfiable by mongodb/mongodb[1.0.0, 1.0.1, 1.0.2, 1.0.3, 1.0.4, 1.0.5, 1.1.0, 1.1.1, 1.1.2, 1.2.0, 1.3.0, 1.3.1, 1.3.2, 1.4.0, 1.4.1, 1.4.2].
- mongodb/mongodb 1.4.2 requires ext-mongodb ^1.5.0 -> the requested PHP extension mongodb is missing from your system.
- mongodb/mongodb 1.4.1 requires ext-mongodb ^1.5.0 -> the requested PHP extension mongodb is missing from your system.
- mongodb/mongodb 1.4.0 requires ext-mongodb ^1.5.0 -> the requested PHP extension mongodb is missing from your system.
- mongodb/mongodb 1.3.2 requires ext-mongodb ^1.4.0 -> the requested PHP extension mongodb is missing from your system.
- mongodb/mongodb 1.3.1 requires ext-mongodb ^1.4.0 -> the requested PHP extension mongodb is missing from your system.
- mongodb/mongodb 1.3.0 requires ext-mongodb ^1.4.0 -> the requested PHP extension mongodb is missing from your system.
- mongodb/mongodb 1.2.0 requires ext-mongodb ^1.3.0 -> the requested PHP extension mongodb is missing from your system.
- mongodb/mongodb 1.1.2 requires ext-mongodb ^1.2.0 -> the requested PHP extension mongodb is missing from your system.
- mongodb/mongodb 1.1.1 requires ext-mongodb ^1.2.0 -> the requested PHP extension mongodb is missing from your system.
- mongodb/mongodb 1.1.0 requires ext-mongodb ^1.2.0 -> the requested PHP extension mongodb is missing from your system.
- mongodb/mongodb 1.0.5 requires ext-mongodb ^1.1.0 -> the requested PHP extension mongodb is missing from your system.
- mongodb/mongodb 1.0.4 requires ext-mongodb ^1.1.0 -> the requested PHP extension mongodb is missing from your system.
- mongodb/mongodb 1.0.3 requires ext-mongodb ^1.1.0 -> the requested PHP extension mongodb is missing from your system.
- mongodb/mongodb 1.0.2 requires ext-mongodb ^1.1.0 -> the requested PHP extension mongodb is missing from your system.
- mongodb/mongodb 1.0.1 requires ext-mongodb ^1.1.0 -> the requested PHP extension mongodb is missing from your system.
- mongodb/mongodb 1.0.0 requires ext-mongodb ^1.1.0 -> the requested PHP extension mongodb is missing from your system.
- Installation request for jenssegers/mongodb ^3.4 -> satisfiable by jenssegers/mongodb[v3.4.0, v3.4.1, v3.4.2].
To enable extensions, verify that they are enabled in your .ini files:
- /usr/local/etc/php/7.1/php.ini
- /usr/local/etc/php/7.1/conf.d/ext-opcache.ini
You can also run `php --ini` inside terminal to see which files are used by PHP in CLI mode.
Installation failed, reverting ./composer.json to its original content.
可以看出，这一步说的是该扩展依赖PHP的MongoDB扩展，那我们动手装上就是了。
macOS系统安装PHP的MongoDB扩展
上次说了，我目前的开发环境是直接用Homebrew安装的Nginx、PHP、MySQL等组件，之前是可以直接用brew安装相应的PHP扩展的，比如说：
brew install php71-mongodb
但是从Homebrew 1.5.0开始，这种方法被遗弃了，会提示Error: No available formula with the name “php71-mongodb”。如果系统不自带相应的扩展，就需要我们手动使用pecl安装，根据PHP官方文档，在macOS/Linux/Unix系统下，只需这一行命令即可：
sudo pecl install mongodb
当然，那只是一般情况，在国内特色网络情况下，如果直接运行很可能会因为网络原因而报错，建议挂个命令行dl再进行安装试试。如果实在是下载不下来，也可以到这里下载对应版本的源码包进行手动安装。
如果自动安装成功，最终看到会有这么一段输出：
Build process completed successfully
Installing '/usr/local/Cellar/php@7.1/7.1.22/pecl/20160303/mongodb.so'
install ok: channel://pecl.php.net/mongodb-1.5.3
Extension mongodb enabled in php.ini
既然成功了，PHP里面肯定会有对应的MongoDB模块了，命令行下使用php -m可以列出所有已安装的模块。
接下来，再次运行上面哪行composer安装命令：
zocoMac:laravel-test zoco$ composer require jenssegers/mongodb
Using version ^3.4 for jenssegers/mongodb
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.
Problem 1
- Conclusion: don't install jenssegers/mongodb v3.4.2
- Conclusion: don't install jenssegers/mongodb v3.4.1
- Conclusion: remove laravel/framework v5.5.43
- Installation request for jenssegers/mongodb ^3.4 -> satisfiable by jenssegers/mongodb[v3.4.0, v3.4.1, v3.4.2].
- Conclusion: don't install laravel/framework v5.5.43
- jenssegers/mongodb v3.4.0 requires illuminate/events ^5.6 -> satisfiable by illuminate/events[v5.6.0, v5.6.1, v5.6.10, v5.6.11, v5.6.12, v5.6.13, v5.6.14, v5.6.15, v5.6.16, v5.6.17, v5.6.19, v5.6.2, v5.6.20, v5.6.21, v5.6.22, v5.6.23, v5.6.24, v5.6.25, v5.6.26, v5.6.27, v5.6.28, v5.6.29, v5.6.3, v5.6.30, v5.6.31, v5.6.32, v5.6.33, v5.6.34, v5.6.35, v5.6.36, v5.6.37, v5.6.38, v5.6.4, v5.6.5, v5.6.6, v5.6.7, v5.6.8, v5.6.9, v5.7.0, v5.7.1, v5.7.2, v5.7.3, v5.7.4, v5.7.5].
- don't install illuminate/events v5.6.0|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.1|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.10|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.11|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.12|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.13|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.14|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.15|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.16|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.17|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.19|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.2|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.20|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.21|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.22|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.23|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.24|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.25|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.26|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.27|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.28|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.29|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.3|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.30|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.31|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.32|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.33|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.34|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.35|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.36|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.37|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.38|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.4|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.5|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.6|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.7|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.8|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.6.9|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.7.0|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.7.1|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.7.2|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.7.3|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.7.4|don't install laravel/framework v5.5.43
- don't install illuminate/events v5.7.5|don't install laravel/framework v5.5.43
- Installation request for laravel/framework (locked at v5.5.43, required as 5.5.*) -> satisfiable by laravel/framework[v5.5.43].
放狗搜了一把也没找到问题出在哪里，但是无意中发现了一个解决办法，就是安装指定版本的jenssegers/mongodb，由于我的Laravel版本为5.5.x，最好的就是安装3.3.x版本的jenssegers/mongodb，命令如下：
composer require jenssegers/mongodb=3.3.*
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Package operations: 2 installs, 0 updates, 0 removals
- Installing mongodb/mongodb (1.4.2): Downloading (100%)
- Installing jenssegers/mongodb (v3.3.1): Downloading (100%)
jenssegers/mongodb suggests installing jenssegers/mongodb-session (Add MongoDB session support to Laravel-MongoDB)
jenssegers/mongodb suggests installing jenssegers/mongodb-sentry (Add Sentry support to Laravel-MongoDB)
Writing lock file
Generating optimized autoload files
> Illuminate\Foundation\ComposerScripts::postAutoloadDump
> @php artisan package:discover
Discovered Package: fideloper/proxy
Discovered Package: jenssegers/mongodb
Discovered Package: laravel/tinker
Discovered Package: nesbot/carbon
Package manifest generated successfully.
这下终于成功安装了jenssegers/mongodb。
后来查看jenssegers/mongodb文档的时候才发现，在jenssegers/mongodb文档安装命令下面就列出了相应的Laravel兼容版本，只是自己太大意没有仔细看文档：
Laravel version Compatibility
| Laravel | Package |
|---|---|
| 4.2.x | 2.0.x |
| 5.0.x | 2.1.x |
| 5.1.x | 2.2.x or 3.0.x |
| 5.2.x | 2.3.x or 3.0.x |
| 5.3.x | 3.1.x or 3.2.x |
| 5.4.x | 3.2.x |
| 5.5.x | 3.3.x |
| 5.6.x | 3.4.x |
根据这个表格，哪个版本的Laravel安装哪个版本的jenssegers/mongodb开发者都有明确的说明，如果你的Laravel版本和我的不一致，可能需要在上述安装命令后面更改成对应的版本号。