I have the following code on typescript playground and a few questions come up that I am not sure how to get working
class PathInfo {
functionName: string;
httpPath: string;
httpMethod: string;
constructor(functionName: string, httpPath: string, httpMethod: string) {
this.functionName = functionName;
this.httpPath = httpPath;
this.httpMethod = httpMethod;
}
toString(): string {
return "PathInfo["+this.functionName+","+this.httpPath+","+this.httpMethod+"]";
}
}
class AuthRequest {}
class AuthResponse {}
class LoginRequest {}
class LoginResponse {}
const path: any = (thePath: string, type: any) => {
return (target: Function, memberName: string, propertyDescriptor: PropertyDescriptor) => {
const pathMeta = new PathInfo(memberName, path, type);
Object.defineProperty(target, memberName+'pathInfo', {
value: pathMeta,
writable: false
});
//How do I access the stored pathMeta
//console.log("target="+target.pathInfo);
console.log("member="+memberName);
console.log("props="+propertyDescriptor);
}
}
class AuthApiImpl {
#path("/authenticate", AuthResponse)
authenticate(request: AuthRequest): Promise<AuthResponse> {
throw new Error("all this is generated by factory.createApiImpl");
}
#path("/login", LoginResponse)
login(request: LoginRequest): Promise<LoginResponse> {
throw new Error("all this is generated by factory.createApiImpl");
}
};
function printMethods(obj: any) {
console.log("starting to print methods");
for (var id in obj) {
console.log("id="+id);
try {
//How do I access the stored pathMeta here FOR EACH METHOD ->
//console.log("target="+target.pathInfo);
if (typeof(obj[id]) == "function") {
console.log(id+":"+obj[id].toString());
}
} catch (err) {
console.log(id + ": inaccessible"+err);
}
}
}
console.log("starting to run")
const temp = new AuthApiImpl();
printMethods(temp);
console.log("done")
line 64-65, how to read the property that I set
line 40-41, how to read the property that I set
line 58-74, why is this not printing any functions? I want to print all functions and I do NOT want to print properties (just functions)
line 33, Can I access the class name at this point?
line 35, I thought target was a function and would be authorize, then login, BUT if I define the property as JUST 'pathInfo', I get an error that the property is already defined on the target(This implies the target is the class not the function?). I am so confused.
Terribly sorry as I try to focus on a single question, but this one test of writing decorators has given me more questions than answers as I delve into the typescript world.
How can I tweak the code to play more here?
A goal here is as developers define the APIs of other microservices, I can capture a bunch of meta information and store it SOMEWHERE I can use later in startup code. I do not care where I store that really, but just need a clean way of knowing the class I want to extend, the methods, the return types, the http path, etc.
How to get methods of a class
You still can't grab the method names even if you remove the decorator. This isn't a TypeScript specific question.
You need to get the properties of the prototype, not just the object itself.
function printMethods(obj: any) {
console.log("starting to print methods");
const objProto = Object.getPrototypeOf(obj);
console.log(Object.getOwnPropertyNames(objProto));
}
How to access class names
Don't think this is possible with decorators at the moment, but it should be straightforward to just pass in your class name as a string.
Similar issue: TypeScript class decorator get class name
Open issue on GitHub: https://github.com/microsoft/TypeScript/issues/1579
"property is already defined on the target"
Notice if you run the code above you get the following in console.log:
["constructor", "authenticate", "login", "authenticatepathInfo", "loginpathInfo"]
I also want to point out that if you don't even initialize an instance of the class, you'll still get the same error.
I want to read this meta data in nodejs and use that to dynamically create a client implementing the api. Basically, developers never have to write clients and only write the api and the implementation is generated for them.
If I were to do that, I'd probably not use decorators, but mapped types:
// library code
interface ApiMethodInfo {
httpPath: string;
httpMethod: string;
}
type ApiInfo<S extends object> = Record<keyof S, ApiMethodInfo>;
type Client<S extends object> = {[key in keyof S]: S[key] extends (req: infer Req) => infer Res ? (req: Req) => Promise<Res> : never};
function generateClient<S extends object>(apiInfo: ApiInfo<S>): Client<S> {
const client = {} as Client<S>;
for (const key in apiInfo) {
const info = apiInfo[key as keyof S];
client[key] = ((param: any) => invokeApi(info, param)) as any;
}
return client;
}
// application code
interface AuthRequest {}
interface AuthResponse {}
interface LoginRequest {
username: string,
password: string,
}
interface LoginResponse {}
interface MyServer {
authenticate(request: AuthRequest): AuthResponse;
login(request: LoginRequest): LoginResponse;
}
const myApiInfo: ApiInfo<MyServer> = { // compiler verifies that all methods of MyServer are described here
authenticate: {
httpPath: '/authenticate',
httpMethod: 'POST'
},
login: {
httpPath: '/login',
httpMethod: 'POST'
}
}
const myClient = generateClient(myApiInfo); // compiler derives the method signatures from the server implementation
const username = "joe";
const password = "secret";
const response = myClient.login({username, password}); // ... and can therefore check that this call is properly typed
(To understand how these type definitions work, you may want to read the section Creating Types from Types in the TypeScript Handbook)
The weakness of this approach is that while the compiler can derive the client signatures from the server signatures, it will not copy any JSDoc, so client devs can not easily access the API documentation.
In the above code, I chose to specify the metadata in a separate object rather than decorators so the compiler can check exhaustiveness (decorators are always optional; the compiler can not be instructed to require their presence), and because decorators are an experimental language feature that may still change in future releases of the language.
It is entirely possible to populate such a metadata object using decorators if that's what you prefer. Here's what that would look like:
// library code
interface ApiMethodInfo {
httpPath: string;
httpMethod: string;
}
const apiMethodInfo = Symbol("apiMethodInfo");
function api(info: ApiMethodInfo) {
return function (target: any, propertyKey: string) {
target[apiMethodInfo] = target[apiMethodInfo] || {};
target[apiMethodInfo][propertyKey] = info;
}
}
type ApiInfo<S extends object> = Record<keyof S, ApiMethodInfo>;
type Client<S extends object> = {[key in keyof S]: S[key] extends (req: infer Req) => infer Res ? (req: Req) => Promise<Res> : never};
function invokeApi(info: ApiMethodInfo, param: any) {
console.log(info, param);
}
function generateClient<S extends object>(serverClass: new() => S): Client<S> {
const infos = serverClass.prototype[apiMethodInfo]; // a decorator's target is the constructor function's prototype
const client = {} as Client<S>;
for (const key in infos) { // won't encounter apiMethodInfo because Symbol properties are not enumerable
const info = infos[key];
client[key as keyof S] = ((param: any) => invokeApi(info, param)) as any;
}
return client;
}
// application code
interface AuthRequest {}
interface AuthResponse {}
interface LoginRequest {
username: string,
password: string,
}
interface LoginResponse {}
class MyServer {
#api({
httpPath: '/authenticate',
httpMethod: 'POST'
})
authenticate(request: AuthRequest): AuthResponse {
throw new Error("Not implemented yet");
}
#api({
httpPath: '/login',
httpMethod: 'POST'
})
login(request: LoginRequest): LoginResponse {
throw new Error("Not implemented yet");
}
}
const myClient = generateClient(MyServer); // compiler derives the method signatures from the server implementation
const username = "joe";
const password = "secret";
const response = myClient.login({username, password}); // ... and can therefore check that this call is properly typed
Notice how using a Symbol prevents name collisions, and ensures that other code doesn't see this property (unless they look for that particular Symbol), and therefore can not be tripped up by its unexpected presence.
Also notice how MyServer, at runtime, contains the constructor of the class, whose prototype holds the declared instance methods, and it being passed as target to any decorators thereof.
General Advice
May I conclude with some advice for the recovering Java programmer? ;-)
EcmaScript is not Java. While the syntax may look similar, EcmaScript has many useful features Java does not, which often allow writing far less code. For instance, if you need a DTO, it is wholly unnecessary to declare a class with a constructor manually copying each parameter into a property. You can simply declare an interface instead, and create the object using an object literal. I recommend looking through the Modern JavaScript Tutorial to familiarize yourself with these useful language features.
Also, some features behave differently in EcmaScript. In particular, the distinction between class and interface is quite different: Classes are for inheriting methods from a prototype, interfaces for passing data around. It's quite nonsensical to declare a class for a Response that will be deserialized from JSON, because prototypes don't survive serialization.
I have the following generic interface in my typescript code:
interface BaseResponse<T> {
status_code: string;
data: T;
}
I thought I would be able to use that base interface, without specifying the base's type parameter, in a generic function like this:
class MyService {
static async post<T extends BaseResponse>(path: string, data: any): Promise<T> {
// implementation here
}
}
But this gives the following error:
Generic type 'BaseResponse<T>' requires 1 type argument(s).(2314)
I can fix this error by updating the code like so:
class MyService {
static async post<T extends BaseResponse<U>, U>(path: string, data: any): Promise<T> {
// implementation here
}
}
But this requires me to pass two type parameters when I call the function as below. I was hoping I could only pass one and it could infer the second, but that gives me the error Expected 2 type arguments, but got 1.(2558). Is there any way to accomplish this?
// What I want to be able to do (Causes error mentioned above):
const response1 = await MyService.post<CustomerResponse>('/customers', postData);
// What I have to do instead (note the two type parameters)
const response2 = await MyService.post<CustomerResponse, CustomerData>('/customers', postData);
The idea is to allow a call to the .build() method only upon having all the mandatory parameters filled. So the constructor should be taught to do some validation.
If I understand you correctly, you have some kind of builder class, which by default doesn't have all the required parameters. And that class has a method, which updates its state. Only when all required parameters are set, only then build method should be available.
So first of all, we have T type which partial (all properties are optional).
On each update, we should return a new instance with type T & Record<K, T[K]> - it means optional T + one non-optional property.
Finally, we can use conditional types to allow build only when T extends Required<T>.
So the final solution:
function createBuilder<T>(initialData: T) {
return {
update: <K extends keyof T>(key: K, value: T[K]) => {
return createBuilder<T & Record<K, T[K]>>({
...initialData,
[key]: value
})
},
build: (() => {
//
}) as T extends Required<T> ? () => boolean : undefined
}
}
const builder1 = createBuilder<Partial<{
key1: string,
key2: number
}>>({})
builder1.build()
// Cannot invoke an object which is possibly 'undefined'
const builder2 = builder1.update('key1', 'abc')
builder2.build()
// Cannot invoke an object which is possibly 'undefined'
const builder3 = builder2.update('key2', 10)
builder3.build()
// No error
Hovewer, there is no point having this logic. If you can statically update the object, you probably can set all properties in the constructor.
I'm working on a groovy method to look for a custom attribute and return the value if the key is found.
The problem is that the method is returning the type of value instead of the value.
// There is more code before, but its not involved with this issue.
def UUIDca = 'UUID'
String customAttributeValue = grabCustomAttribute(UUIDca, event_work)
appendLogfile("\n\nTest grabCustomAttribute: ${customAttributeValue}\n")
}
// Grab the Custom Message Attribute values by name
String grabCustomAttribute (String findElement, OprEvent event){
appendLogfile("""\nIN grabCustomAttribute\nElement to look: ${findElement}\n""")
def firstItem = true
if (event.customAttributes?.customAttributes?.size()) {
event.customAttributes.customAttributes.each { ca ->
// Define each CMA to catch here
appendLogfile("""\nElement: ${ca.name} - """)
appendLogfile("""Valor: ${ca.value}\n""")
if ("${ca.name}" == findElement) {
String customValue = ca.value
appendLogfile("""Custom Attribute Found\n""")
appendLogfile(customValue)
return customValue
}
}
}
}
appendLogfile is basically a print to a log file :)
This is the output I'm getting.
IN grabCustomAttribute Element to look: UUID
Element: UUID - Valor: c3bb9169-0ca3-4bcf-beb1-f94eda8ebf1a
Custom Attribute Found
c3bb9169-0ca3-4bcf-beb1-f94eda8ebf1a
Test grabCustomAttribute: [com.hp.opr.api.ws.model.event.OprCustomAttribute#940e503a]
Instead of returning the value, it returns the type of object. It's correct, but I'm looking for the value.
I believe the solution is really simple, but I'm very new to Groovy.
Any help will be appreciated.
Thanks.
In this case the return statement is for the closure, not for the method, so your method is actually returning the list that "each" is iterating over
The easiest approach you can take here is to use Groovy find method to find the element you are searching for. Something like this:
String grabCustomAttribute (String findElement, OprEvent event) {
return event.customAttributes.customAttributes?.find { ca -> ca.name == findElement }.value
}
I want to use MappedTo[String] as one column type. There is one query using like to select some records.
Sample code:
case class ID(value: String) extends scala.slick.lifted.MappedTo[String]
class Order(tag: Tag) extends Table[(ID, String)](tag, "order") {
def id = column[ID]("id", O.PrimaryKey)
def name = column[String]("name", O.NotNull)
def * = (id, name)
}
val ordres = TableQuery[Order]
def all(implicit session: Session) = {
ordres.filter(_.id like "2014.%").list
}
Compiler error:
[error] value like is not a member of scala.slick.lifted.Column[models.ID]
[error] ordres.filter(_.id like "2014.%").list
[error] ^
[error] ambiguous implicit values:
[error] both value BooleanColumnCanBeQueryCondition in object CanBeQueryCondition of type => scala.slick.lifted.CanBeQueryCondition[scala.slick.lifted.Column[Boolean]]
[error] and value BooleanOptionColumnCanBeQueryCondition in object CanBeQueryCondition of type => scala.slick.lifted.CanBeQueryCondition[scala.slick.lifted.Column[Option[Boolean]]]
[error] match expected type scala.slick.lifted.CanBeQueryCondition[Nothing]
[error] ordres.filter(_.id like "2014.%").list
How to fix it? Thanks.
The only solution I currently found, is to resort to sql interpolated strings
//slick needs this to be able to convert to your custom wrapper type
implicit val GetID = GetResult(r => ID(r.nextString))
def all(implicit session: Session) = {
sql"""select id, name from order where id like '2014.%'""").list
}
As a sidenote there is also a startsWith method that can be used in filtering strings with lifted embedding, and it would've been more appropriate for your case; that is, if filter worked as expected.
You should override the value definition. See this answer
case class ID(id: String) extends scala.slick.lifted.MappedTo[String] {
override def value: String = id
}