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Using custom function template
with AWS Amplify
Masahiko Murakami (@fossamagna) ESM, Inc. | 2021-11-20
Amplify Japan User Grou
p
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Introductions
Masahiko Murakam
i
• Software Developer - ESM, Inc
.
• Amplify Japan User Group Core Membe
r
• Background
:
• TypeScript/JavaScrip
t
• Node.j
s
• Jav
a
• Twitter: https://twitter.com/fossamagna
• GitHub: https://github.com/fossamagna
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Agenda
•What is AWS Amplify function template
?
•Authoring a custom function templat
e
•Third-party function templates
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What is AWS Amplify
function template?
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What is AWS Amplify function template?
• Function template is resources
that are added by executing the
amplify function add
comman
d
• Lambda source code (ex: *.js,
*.py, *.go *.java, *cs
)
• Exclude CloudFormation
template
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What is AWS Amplify function template?
• Amplify function template is
plugin for amplify cl
i
• util plugi
n
• Plugin name is named
functionTemplate
• Template meta information is
defined in functionTemplate of
amplify-plugin.json
• Implements
functionTemplateContributo
rFactory function
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Authoring a custom
function template
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Authoring a custom function template
The specification of custom function template plugi
n
• Generate AppSync Lambda Resolve
r
• Supported Lambda runtime is Node.j
s
• User can select GraphQL fields in schema.graphql to
associate resolver
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Authoring a custom function template
Implementation step
s
1.Run amplify plugin ini
t
2.Edit amplify-plugin.jso
n
3.Implements functionTemplateContributorFactory functio
n
4.Implements source code templates with EJS templat
e
5.Implements additional questions for user (Optional)
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Run amplify plugin init
• Run amplify plugin init
• Input name of the custom function template plugin (ex: amplify-appsync-
resolver-nodejs-function-template-provider
)
• Select util plugin as typ
e
• Clear all selections for event handle
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Edit amplify-plugin.json
• Set the name attribute to
functionTemplate
• Define the functionTemplate
attribut
e
• The conditions attribute defines the
conditions to which the template
applie
s
• The templates attribute defines a list
of user-selectable templates on the CLI
{
"name": "functionTemplate",
"type": “util",
"commands": [],
"eventHandlers": [],
"functionTemplate": {
"conditions": {
"provider": "awscloudformation",
"services": ["Lambda"],
"runtime": "nodejs"
},
"templates": [
{
"name": "AppSync Lambda Resolver",
"value": "resolver"
}
]
}
}
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Implements
functionTemplateContributorFactory function
• Implement a function named
functionTemplateContributor
Factory in index.ts
• functionTemplateContributor
Factory function takes a context
as an argument and returns an
object with contribute functio
n
• contribute function is a function
that takes a
TemplateContributionRequest
as an argument and returns a
Partial
export const functionTemplateContributorFactory: FunctionTemplateContributorFactory =
(context) => {
return {
contribute: (request) => {
switch (request.selection) {
case 'resolver': {
const resolvers = await askGraphQLFieldsQuestions(context);
const files = fs.readdirSync(pathToTemplateFiles);
return Promise.resolve({
functionTemplate: {
sourceRoot: pathToTemplateFiles,
sourceFiles: files,
defaultEditorFile: path.join('src', 'index.js'),
destMap: getDstMap(files),
parameters: { resolvers }
},
});
}
default: {
throw new Error(`Unknown template selection [${request.selection}]`);
}
}
}
}
};
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Implements source code templates with
EJS template
• Templates can be written in EJ
S
• In the EJS template, the return
value of the contribute
function can be accessed with
the props variabl
e
• This can be used to query the
user and reflect the entered
value in a file that outputs
/**
* Using this as the entry point, you can use a single function to handle many
resolvers.
*/
const resolvers = {<% for(var resolver of
props.functionTemplate.parameters.resolvers) { %>
<%= resolver.name %>: {<% for(var fieldResolver of resolver.fieldResolvers)
{ %>
<%= fieldResolver.name %>: ctx => {
// Add your code here
},<% } %>
},<% } %>
}
exports.handler = async (event) => {
const typeHandler = resolvers[event.typeName];
if (typeHandler) {
const resolver = typeHandler[event.fieldName];
if (resolver) {
return await resolver(event);
}
}
throw new Error("Resolver not found.");
};
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Using custom function template plugin
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Third-party function
templates
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Third-party function templates
• https://github.com/thorsten-stripe/amplify-stripe-
nodejs-function-template-provider
• https://github.com/fossamagna/amplify-appsync-
resolver-nodejs-function-template-provider
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Thank you!