Schema 教程第30课：将内容从上游分发到多个下游站点
第30课：将内容从上游分发到多个下游站点
假设一家媒体公司拥有针对不同地区的 WordPress 站点网络，每篇新闻文章只有在适合该地区时才会发布到相应站点。
对于这种情况，实现以下架构是合理的：
- 所有内容发布到（并在）单一上游 WordPress 站点中进行编辑，该站点作为内容的唯一真实来源
- 适当的内容分发到各个地区的下游 WordPress 站点（但不在其中编辑）
本教程课程将演示如何实现此架构：上游 WordPress 站点需要激活相关的 Gato GraphQL 扩展，而下游站点只需安装免费的 Gato GraphQL 插件。
将内容从上游同步到下游站点的 GraphQL Query
（仅限下游站点） 若要使此 GraphQL query 正常工作，应用于端点的架构配置需要启用嵌套 Mutation
以下 GraphQL query 在上游 WordPress 站点上执行，使用文章 slug 作为跨站点的通用标识符，将已更新文章的内容同步到相关的下游站点。
（如前一教程课程所述，该 query 也可以进行调整，以同步其他属性——标签、分类、作者和特色图片。）
该 query 包含事务逻辑，因此当任何下游站点上的更新失败时——无论是 HTTP 请求失败（例如服务器宕机）还是 GraphQL query 产生错误（例如不存在具有所提供 slug 的文章）——所有下游站点上的 mutation 都会被撤销。
要撤销状态，必须提供变量 $previousPostContent。我们可以通过挂钩 WordPress 的 post_updated 动作来传递此值，该动作触发时会执行 GraphQL query（如前一教程课程所述）。
该 query 执行以下操作：
- 接收已更新文章的 slug 及其新内容和旧内容
- 从文章中检索元属性
"downstream_domains"，其中包含文章需要分发到的下游站点域名数组 - 如果元属性不存在（即其值为
null），则从wp_options表中检索选项"downstream_domains"，其中包含所有下游域名的列表 - 将用户登录到每个下游站点（为简便起见使用相同的
$username和$userPassword）并执行 mutation 以更新文章内容 - 如果任何下游站点产生错误，则在所有下游站点上撤销该 mutation
query InitializeDynamicVariables
@configureWarningsOnExportingDuplicateVariable(enabled: false)
{
initVariablesWithFalse: _echo(value: false)
@export(as: "requestProducedErrors")
@export(as: "anyErrorProduced")
@export(as: "hasDownstreamDomains")
@remove
}
query GetCustomDownstreamDomains($postSlug: String!)
@depends(on: "InitializeDynamicVariables")
{
post(by: { slug: $postSlug }, status: any)
@fail(
message: "There is no post in the upstream site with the provided slug"
data: {
slug: $postSlug
}
)
{
customDownstreamDomains: metaValues(key: "downstream_domains")
@export(as: "downstreamDomains")
hasDefinedCustomDownstreamDomains: _notNull(value: $__customDownstreamDomains)
@export(as: "hasDefinedCustomDownstreamDomains")
@remove
hasCustomDownstreamDomains: _notEmpty(value: $__customDownstreamDomains)
@export(as: "hasDownstreamDomains")
}
isMissingPostInUpstream: _isNull(value: $__post)
@export(as: "isMissingPostInUpstream")
}
query GetAllDownstreamDomains
@depends(on: "GetCustomDownstreamDomains")
@skip(if: $isMissingPostInUpstream)
@skip(if: $hasDefinedCustomDownstreamDomains)
{
allDownstreamDomains: optionValues(name: "downstream_domains")
@export(as: "downstreamDomains")
hasAllDownstreamDomains: _notEmpty(value: $__allDownstreamDomains)
@export(as: "hasDownstreamDomains")
}
############################################################
# (By default) Append "/graphql" to the domain, to point
# to that site's GraphQL single endpoint
############################################################
query ExportDownstreamGraphQLEndpointsAndQuery(
$endpointPath: String! = "/graphql"
)
@depends(on: "GetAllDownstreamDomains")
@skip(if: $isMissingPostInUpstream)
@include(if: $hasDownstreamDomains)
{
downstreamGraphQLEndpoints: _echo(value: $downstreamDomains)
@underEachArrayItem(
passValueOnwardsAs: "domain"
)
@strAppend(string: $endpointPath)
@export(as: "downstreamGraphQLEndpoints")
query: _echo(value: """
mutation LoginUserAndUpdatePost(
$username: String!
$userPassword: String!
$postSlug: String!
$postContent: String!
) {
loginUser(by: {
credentials: {
usernameOrEmail: $username,
password: $userPassword
}
}) {
userID
}
post(by: {slug: $postSlug})
@fail(
message: "There is no post in the downstream site with the provided slug"
data: {
slug: $postSlug
}
)
{
update(input: {
contentAs: { html: $postContent },
}) {
status
errors {
__typename
...on ErrorPayload {
message
}
}
post {
slug
rawContent
}
}
}
}
"""
)
@export(as: "query")
@remove
}
query ExportSendGraphQLHTTPRequestInputs(
$username: String!
$userPassword: String!
$postSlug: String!
$newPostContent: String!
)
@depends(on: "ExportDownstreamGraphQLEndpointsAndQuery")
@skip(if: $isMissingPostInUpstream)
@include(if: $hasDownstreamDomains)
{
sendGraphQLHTTPRequestInputs: _echo(value: $downstreamGraphQLEndpoints)
@underEachArrayItem(
passValueOnwardsAs: "endpoint"
)
@applyField(
name: "_echo",
arguments: {
value: {
endpoint: $endpoint,
query: $query,
variables: [
{
name: "username",
value: $username
},
{
name: "userPassword",
value: $userPassword
},
{
name: "postSlug",
value: $postSlug
},
{
name: "postContent",
value: $newPostContent
}
]
}
},
setResultInResponse: true
)
@export(as: "sendGraphQLHTTPRequestInputs")
@remove
}
query SendGraphQLHTTPRequests
@depends(on: "ExportSendGraphQLHTTPRequestInputs")
@skip(if: $isMissingPostInUpstream)
@include(if: $hasDownstreamDomains)
{
downstreamGraphQLResponses: _sendGraphQLHTTPRequests(
inputs: $sendGraphQLHTTPRequestInputs
)
@export(as: "downstreamGraphQLResponses")
requestProducedErrors: _isNull(value: $__downstreamGraphQLResponses)
@export(as: "requestProducedErrors")
@export(as: "anyErrorProduced")
@remove
}
query ExportGraphQLResponsesHaveErrors
@depends(on: "SendGraphQLHTTPRequests")
@skip(if: $isMissingPostInUpstream)
@skip(if: $requestProducedErrors)
@include(if: $hasDownstreamDomains)
{
graphQLResponsesHaveErrors: _echo(value: $downstreamGraphQLResponses)
# Check if any GraphQL response has the "errors" entry
@underEachArrayItem(
passValueOnwardsAs: "response"
affectDirectivesUnderPos: [1, 2]
)
@applyField(
name: "_propertyIsSetInJSONObject"
arguments: {
object: $response
by: {
key: "errors"
}
}
setResultInResponse: true
)
@export(as: "graphQLResponsesHaveErrors")
@remove
}
query ValidateGraphQLResponsesHaveErrors
@depends(on: "ExportGraphQLResponsesHaveErrors")
@skip(if: $isMissingPostInUpstream)
@skip(if: $requestProducedErrors)
@include(if: $hasDownstreamDomains)
{
anyGraphQLResponseHasErrors: _or(values: $graphQLResponsesHaveErrors)
@export(as: "anyErrorProduced")
@remove
}
query ExportRevertGraphQLHTTPRequestInputs(
$username: String!
$userPassword: String!
$postSlug: String!
$previousPostContent: String!
)
@depends(on: "ValidateGraphQLResponsesHaveErrors")
@include(if: $hasDownstreamDomains)
@include(if: $anyErrorProduced)
{
revertGraphQLHTTPRequestInputs: _echo(value: $downstreamGraphQLEndpoints)
@underEachArrayItem(
passValueOnwardsAs: "endpoint"
)
@applyField(
name: "_echo",
arguments: {
value: {
endpoint: $endpoint,
query: $query,
variables: [
{
name: "username",
value: $username
},
{
name: "userPassword",
value: $userPassword
},
{
name: "postSlug",
value: $postSlug
},
{
name: "postContent",
value: $previousPostContent
}
]
}
},
setResultInResponse: true
)
@export(as: "revertGraphQLHTTPRequestInputs")
@remove
}
query RevertGraphQLHTTPRequests
@depends(on: "ExportRevertGraphQLHTTPRequestInputs")
@skip(if: $isMissingPostInUpstream)
@include(if: $hasDownstreamDomains)
@include(if: $anyErrorProduced)
{
revertGraphQLResponses: _sendGraphQLHTTPRequests(
inputs: $sendGraphQLHTTPRequestInputs
)
}
query ExecuteAll
@depends(on: "RevertGraphQLHTTPRequests")
{
id @remove
}在上述 GraphQL query 中，当文章的元属性 "downstream_domains" 被定义为空数组时，该文章将不会分发到任何下游站点。
这得益于函数字段 _notNull 和 _notEmpty 之间的差异（由 PHP Functions via Schema 扩展提供）：
- 如果元属性
"downstream_domains"未定义，其值为null，_notNull和_notEmpty均评估为false - 如果元属性
"downstream_domains"被定义为空数组，其值为[]，只有_notEmpty评估为false