This is documentation on a preview feature.

状态存储

创建一个状态存储组件只需要几个基本步骤。

导入状态存储包

创建文件components/statestore.go并添加import语句，用于状态存储相关的包。

package components

import (
	"context"
	"github.com/dapr/components-contrib/state"
)

实现 Store 接口

创建一个实现Store接口的类型。

type MyStateStore struct {
}

func (store *MyStateStore) Init(metadata state.Metadata) error {
	// Called to initialize the component with its configured metadata...
}

func (store *MyStateStore) GetComponentMetadata() map[string]string {
    // Not used with pluggable components...
	return map[string]string{}
}

func (store *MyStateStore) Features() []state.Feature {
	// Return a list of features supported by the state store...
}

func (store *MyStateStore) Delete(ctx context.Context, req *state.DeleteRequest) error {
	// Delete the requested key from the state store...
}

func (store *MyStateStore) Get(ctx context.Context, req *state.GetRequest) (*state.GetResponse, error) {
	// Get the requested key value from the state store, else return an empty response...
}

func (store *MyStateStore) Set(ctx context.Context, req *state.SetRequest) error {
	// Set the requested key to the specified value in the state store...
}

func (store *MyStateStore) BulkGet(ctx context.Context, req []state.GetRequest) (bool, []state.BulkGetResponse, error) {
	// Get the requested key values from the state store...
}

func (store *MyStateStore) BulkDelete(ctx context.Context, req []state.DeleteRequest) error {
	// Delete the requested keys from the state store...
}

func (store *MyStateStore) BulkSet(ctx context.Context, req []state.SetRequest) error {
	// Set the requested keys to their specified values in the state store...
}

注册状态存储组件

在主应用程序文件中（例如，main.go），将状态存储注册到应用程序服务中。

package main

import (
	"example/components"
	dapr "github.com/dapr-sandbox/components-go-sdk"
	"github.com/dapr-sandbox/components-go-sdk/state/v1"
)

func main() {
	dapr.Register("<socket name>", dapr.WithStateStore(func() state.Store {
		return &components.MyStateStoreComponent{}
	}))

	dapr.MustRun()
}

批量状态存储

虽然需要状态存储来支持 批量操作，它们的实现按顺序委托给各个操作方法。

事务性状态存储

打算支持事务的状态存储应该实现可选的TransactionalStore接口。 它的Multi()方法接收一个请求，其中包含要在事务中执行的一系列delete和/或set操作。 状态存储应该遍历序列并应用每个操作。

func (store *MyStateStoreComponent) Multi(ctx context.Context, request *state.TransactionalStateRequest) error {
    // Start transaction...

    for _, operation := range request.Operations {
		switch operation.Operation {
		case state.Delete:
			deleteRequest := operation.Request.(state.DeleteRequest)
			// Process delete request...
		case state.Upsert:
			setRequest := operation.Request.(state.SetRequest)
			// Process set request...
		}
	}

    // End (or rollback) transaction...

	return nil
}

可查询的状态存储

打算支持查询的状态存储应该实现可选的Querier接口。 它的Query()方法会传递有关查询的详细信息，例如过滤器、结果限制、分页和结果的排序顺序。 状态存储使用这些详细信息来生成一组值，作为其响应的一部分返回。

func (store *MyStateStoreComponent) Query(ctx context.Context, req *state.QueryRequest) (*state.QueryResponse, error) {
	// Generate and return results...
}

ETag 和其他语义错误处理

Dapr 运行时对某些状态存储操作的特定错误条件有额外处理。 状态存储可以通过从其操作逻辑中返回特定错误来指示这些条件：

错误 适用操作 说明
NewETagError(state.ETagInvalid, ...) Delete, Set, Bulk Delete, Bulk Set 当 ETag 无效时
NewETagError(state.ETagMismatch, ...) Delete, Set, Bulk Delete, Bulk Set 当 ETag 与预期值不匹配时
NewBulkDeleteRowMismatchError(...) Bulk Delete 当受影响的行数与预期的行数不匹配时

下一步