（接上篇）
EdgeCore 之 d evicetwin
前面对EdgeCore组件的edged功能模块进行了分析，本节对EdgeCore组件的另一个功能模块devicetwin进行剖析，包括devicetwin的struct调用链剖析、devicetwin的具体逻辑剖析、devicetwin的缓存机制剖析。
1. devicetwin 的struct调用 链 剖析
从EdgeCore模块注册函数入手，具体如下所示。
|----------------------------------------------------------------------------------------------------------------------|
| KubeEdge/edge/cmd/EdgeCore/app/server.go |
| // registerModules register all the modules started in EdgeCore func registerModules() { devicetwin.Register() ... } |
进入registerModules()函数中的devicetwin.Register()函数定义，具体如下所示。
|-------------------------------------------------------------------------------------------------------------------|
| KubeEdge/edge/pkg/devicetwin/devicetwin.go |
| // Register register devicetwin func Register() { dtclient.InitDBTable() dt := DeviceTwin{} core.Register(&dt) } |
Register()函数主要做了如下3件事。
1）初始化devicetwin需要的数据库表（dtclient.InitDBTable()）；
2）实例化DeviceTwin struct（dt := DeviceTwin{}）；
3）注册将已经实例化的DeviceTwin struct（core.Register(&dt)）。
下面深入剖析初始化devicetwin需要的数据库表具体做了哪些事情以及DeviceTwin struct具体由哪些属性组成。
（1）devicetwin数据库相关struct剖析
这部分剖析初始化devicetwin需要的数据库及数据库表相关的struct，具体如下所示。
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| KubeEdge/edge/pkg/devicetwin/dtclient/sql.go |
| //InitDBTable create table func InitDBTable() { klog.Info("Begin to register twin model") dbm.RegisterModel("twin", new(Device)) dbm.RegisterModel("twin", new(DeviceAttr)) dbm.RegisterModel("twin", new(DeviceTwin)) } |
在InitDBTable()函数中，通过封装的beego的orm(https://GitHub.com/astaxie/beego/tree/develop/orm)创建数据库twin，并初始化device、device_attr和device_twin三张表。与上述三张表对应的结构体如下所示。
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| KubeEdge/edge/pkg/devicetwin/dtclient/device_db.go |
| //Device the struct of device type Device struct { ID string `orm:"column(id); size(64); pk"` Name string `orm:"column(name); null; type(text)"` Description string `orm:"column(description); null; type(text)"` State string `orm:"column(state); null; type(text)"` LastOnline string `orm:"column(last_online); null; type(text)"` } KubeEdge/edge/pkg/devicetwin/dtclient/deviceattr_db.go //DeviceAttr the struct of device attributes type DeviceAttr struct { ID int64 `orm:"column(id);size(64);auto;pk"` DeviceID string `orm:"column(deviceid); null; type(text)"` Name string `orm:"column(name);null;type(text)"` Description string `orm:"column(description);null;type(text)"` Value string `orm:"column(value);null;type(text)"` Optional bool `orm:"column(optional);null;type(integer)"` AttrType string `orm:"column(attr_type);null;type(text)"` Meta Data string `orm:"column(metadata);null;type(text)"` } KubeEdge/edge/pkg/devicetwin/dtclient/devicetwin_db.go //DeviceTwin the struct of device twin type DeviceTwin struct { ID int64 `orm:"column(id);size(64);auto;pk"` DeviceID string `orm:"column(deviceid); null; type(text)"` Name string `orm:"column(name);null;type(text)"` Description string `orm:"column(description);null;type(text)"` Expected string `orm:"column(expected);null;type(text)"` Actual string `orm:"column(actual);null;type(text)"` ExpectedMeta string `orm:"column(expected_meta);null;type(text)"` ActualMeta string `orm:"column(actual_meta);null;type(text)"` ExpectedVersion string `orm:"column(expected_version);null;type(text)"` ActualVersion string `orm:"column(actual_version);null;type(text)"` Optional bool `orm:"column(optional);null;type(integer)"` AttrType string `orm:"column(attr_type);null;type(text)"` Meta Data string `orm:"column(metadata);null;type(text)"` } |
以上3个文件中除了包含与device、device_attr和device_twin三张表对应的结构体定义外，还有针对这三张表的增、删、改、查方法的定义。
「 未完待续...... 」