Hello? I'm building an app using the flutter provider pattern. And I created a process to query the values inside the object. I also have data in my model dart file.
Check the code below.
List<Device> _devices = [
Device(one: 'apple', two: 'iphone'),
Device(one: 'samsung', two: 'galaxy')
];
String Query(String value) {
return _media.where((medium) => medium.one == value)
.map((medium) => (medium.two)).toString();
Query("apple")
So, when I call that function, I expect iphone to be returned. But the results come in (iphne). Actually I know why. After all, the data returned is a List<Device> type. But what I want is to remove the parentheses by returning only the first value in the queried list(meaning only queried list, not the full list). In other words, I want to receive iphone, not (iphone). Currently, I am using substring removing the first and the final word, which seems to have some limitations. Is there any way to remove parentheses in that logic?
You have parentheses because you're calling .toString() on a list:
return _media.where((medium) => medium.one == value)
.map((medium) => (medium.two))
.toString();
To return just .two or the first found object, you just have to do:
return _media.firstWhere(
(medium) => medium.one == value, orElse: () => null)?.two;
That will return the value of .two of the first found object or null if nothing found.
Doc: Iterable.firstWhere()
Related
I've been writing test using sinon. During the same I wrote stub where some input parameters are passed and an object is returned. This object returns some values and a random date value generated by system at the time of execution. So need guidance on following.
How can I handle the same as the matching arguments are static in nature and I don't know the possible value of the date generated by actual code.
How can we skip certain key values of an object using sinon. i.e. say object has following values. const object = {name: "abc", employeeNumber : "123"} I only want to check if name is "abc" and don't need to match employeeNumber.
From the sinon.match docs:
Requires the value to be not null or undefined and have at least the same properties as expectation.
From the sinon.assert.match docs:
Uses sinon.match to test if the arguments can be considered a match.
Example:
test('partial object match', () => {
const object = { name: "abc", employeeNumber : "123" };
sinon.assert.match(object, { name: 'abc' }); // SUCCESS
})
I am working on a react app with react-apollo
calling data through graphql when I check in browser network tab response it shows all elements of the array different
but what I get or console.log() in my app then all elements of array same as the first element.
I don't know how to fix please help
The reason this happens is because the items in your array get "normalized" to the same values in the Apollo cache. AKA, they look the same to Apollo. This usually happens because they share the same Symbol(id).
If you print out your Apollo response object, you'll notice that each of the objects have Symbol(id) which is used by Apollo cache. Your array items probably have the same Symbol(id) which causes them to repeat. Why does this happen?
By default, Apollo cache runs this function for normalization.
export function defaultDataIdFromObject(result: any): string | null {
if (result.__typename) {
if (result.id !== undefined) {
return `${result.__typename}:${result.id}`;
}
if (result._id !== undefined) {
return `${result.__typename}:${result._id}`;
}
}
return null;
}
Your array item properties cause multiple items to return the same data id. In my case, multiple items had _id = null which caused all of these items to be repeated. When this function returns null the docs say
InMemoryCache will fall back to the path to the object in the query,
such as ROOT_QUERY.allPeople.0 for the first record returned on the
allPeople root query.
This is the behavior we actually want when our array items don't work well with defaultDataIdFromObject.
Therefore the solution is to manually configure these unique identifiers with the dataIdFromObject option passed to the InMemoryCache constructor within your ApolloClient. The following worked for me as all my objects use _id and had __typename.
const client = new ApolloClient({
link: authLink.concat(httpLink),
cache: new InMemoryCache({
dataIdFromObject: o => (o._id ? `${o.__typename}:${o._id}`: null),
})
});
Put this in your App.js
cache: new InMemoryCache({
dataIdFromObject: o => o.id ? `${o.__typename}-${o.id}` : `${o.__typename}-${o.cursor}`,
})
I believe the approach in other two answers should be avoided in favor of following approach:
Actually it is quite simple. To understand how it works simply log obj as follows:
dataIdFromObject: (obj) => {
let id = defaultDataIdFromObject(obj);
console.log('defaultDataIdFromObject OBJ ID', obj, id);
}
You will see that id will be null in your logs if you have this problem.
Pay attention to logged 'obj'. It will be printed for every object returned.
These objects are the ones from which Apollo tries to get unique id ( you have to tell to Apollo which field in your object is unique for each object in your array of 'items' returned from GraphQL - the same way you pass unique value for 'key' in React when you use 'map' or other iterations when rendering DOM elements).
From Apollo dox:
By default, InMemoryCache will attempt to use the commonly found
primary keys of id and _id for the unique identifier if they exist
along with __typename on an object.
So look at logged 'obj' used by 'defaultDataIdFromObject ' - if you don't see 'id' or '_id' then you should provide the field in your object that is unique for each object.
I changed example from Apollo dox to cover three cases when you may have provided incorrect identifiers - it is for cases when you have more than one GraphQL types:
dataIdFromObject: (obj) => {
let id = defaultDataIdFromObject(obj);
console.log('defaultDataIdFromObject OBJ ID', obj, id);
if (!id) {
const { __typename: typename } = obj;
switch (typename) {
case 'Blog': {
// if you are using other than 'id' and '_id' - 'blogId' in this case
const undef = `${typename}:${obj.id}`;
const defined = `${typename}:${obj.blogId}`;
console.log('in Blogs -', undef, defined);
return `${typename}:${obj.blogId}`; // return 'blogId' as it is a unique
//identifier. Using any other identifier will lead to above defined problem.
}
case 'Post': {
// if you are using hash key and sort key then hash key is not unique.
// If you do query in DB it will always be the same.
// If you do scan in DB quite often it will be the same value.
// So use both hash key and sort key instead to avoid the problem.
// Using both ensures ID used by Apollo is always unique.
// If for post you are using hashKey of blogID and sortKey of postId
const notUniq = `${typename}:${obj.blogId}`;
const notUniq2 = `${typename}:${obj.postId}`;
const uniq = `${typename}:${obj.blogId}${obj.postId}`;
console.log('in Post -', notUniq, notUniq2, uniq);
return `${typename}:${obj.blogId}${obj.postId}`;
}
case 'Comment': {
// lets assume 'comment's identifier is 'id'
// but you dont use it in your app and do not fetch from GraphQl, that is
// you omitted 'id' in your GraphQL query definition.
const undefnd = `${typename}:${obj.id}`;
console.log('in Comment -', undefnd);
// log result - null
// to fix it simply add 'id' in your GraphQL definition.
return `${typename}:${obj.id}`;
}
default: {
console.log('one falling to default-not good-define this in separate Case', ${typename});
return id;
}
I hope now you see that the approach in other two answers are risky.
YOU ALWAYS HAVE UNIQUE IDENTIFIER. SIMPLY HELP APOLLO BY LETTING KNOW WHICH FIELD IN OBJECT IT IS. If it is not fetched by adding in query definition add it.
An alternative option to the accepted is to instead of dataIdFromObject, which appears to be for everything in the query, I was able to provide a keyFields function per type that required it.
const client = new ApolloClient({
cache: new InMemoryCache({
typePolicies: {
ItemType: {
keyFields: (obj) =>
obj.id + "-" + obj.language.id,
},
},
}),
});
In the above example ItemType can be whichever Type is specified in your schema. I happened to be joining a non-unique ID with a language to make a unique key but you can do it however you wish.
This is a example of what my state looks like:
state = {
messages: [
{name: 'Bruce', content: 'Hello'},
{name: 'Clark', content: 'World'}
]
}
I am writing a reducer that will take the ADD_MESSAGE action and add a message to the message list. I would like to take into account the case where the 'messages' key is not defined. I am just starting to use ImmutableJS.
This is how I wrote my function:
// This is really bad
const addMessage = (state, message) => {
let mutableState = state.toJS();
if(mutableState.messages){
mutableState.messages.push(message);
}else{
mutableState = {messages: [message]}
}
return fromJS(mutableState);
}
I'm pretty sure there is a better way to do that. It should work whether my state argument is Immutable or not. Any idea? Thank you!
This is a possible implementation:
const addMessage = (state, message) =>
state.update('messages', Immutable.List(),
msgs => msgs.push(Immutable.Map(message)));
The 2nd arg passed to update is the default value if the key doesn't exist, and the 3rd argument is a closure to take the current value for the key (or default value) and perform the required update. The code also converts the message into an Immutable.Map, but you might prefer to use an Immutable.Record type.
See https://facebook.github.io/immutable-js/docs/#/Map/update for more info on update. updateIn is also very useful for updating store state, as are set, merge, setIn and mergeIn.
I have few tables in rethinkdb with very varied datasets. Mostly because over time, out of simple string properties complex objects were created to be more expressive.
When I run a query, I'm making sure that all fields exist, with the hasFields - function. But what if I want to run a RegExp query on my Message property, which can be of type string or object. Of course if it is an object, I don't care about the row, but instead of ignoring it, rethinkdb throws the error:
Unhandled rejection RqlRuntimeError: Expected type STRING but found OBJECT in...
Can I somehow use typeOf to first determine the type, before running the query?
Or what would be a good way to do this?
Your question is not 100% clear to me so I'm going to restate the problem to make sure my solution gets sense.
Problem
Get all documents where the message property is of type object or the message property is a string and matches a particular regular expression (using the match method).
Solution
You basically need an if statement. For that, you can use the r.branch to 'branch' your conditions depending on these things.
Here's a very long, but clear example on how to do this:
Let's say you have these documents and you want all documents where the message property is an object or a string that has the substring 'string'. The documents look like this:
{
"id": "a1a17705-e7b0-4c84-b9d5-8a51f4599eeb" ,
"message": "invalid"
}, {
"id": "efa3e26f-2083-4066-93ac-227697476f75" ,
"message": "this is a string"
}, {
"id": "80f55c96-1960-4c38-9810-a76aef60d678" ,
"not_messages": "hello"
}, {
"id": "d59d4e9b-f1dd-4d23-a3ef-f984c2361226" ,
"message": {
"exists": true ,
"text": "this is a string"
}
}
For that , you can use the following query:
r.table('messages')
.hasFields('message') // only get document with the `message` property
.filter(function (row) {
return r.branch( // Check if it's an object
row('message').typeOf().eq('OBJECT'), // return true if it's an object
true,
r.branch( // Check if it's a string
row('message').typeOf().eq('STRING'),
r.branch( // Only return true if the `message` property ...
row('message').match('string'), // has the substring `string`
true,
false // return `false` if it's a string but doesn't match our regex
),
false // return `false` if it's neither a string or an object
)
)
})
Again this query is long and could be written a lot more elegantly, but it explains the use of branch very clearly.
A shorter way of writing this query is this:
r.table('messages')
.hasFields('message')
.filter(function (row) {
return
row('message').typeOf().eq('OBJECT')
.or(
row('message').typeOf().eq('STRING').and(row('message').match('string'))
)
})
This basically uses the and and or methods instead of branch.
This query will return you all registers on table message that have the field message and the field is String.
Cheers.
r.db('test').table('message').hasFields('message')
.filter(function (row) {
return row('message').typeOf().eq('STRING')
})
I'm pretty new to scala and basically I want to have a couple of functions coupled to a string in a hashmap.
However I get an error at subscribers.get(e.key)(e.EventArgs); stating Option[EventArgs => Unit] does not take parameters...
Example code:
object Monitor {
val subscribers = HashMap.empty[String, (EventArgs) => Unit ]
def trigger(e : Event){
subscribers.get(e.key)(e.EventArgs);
}
def subscribe(key: String, e: (EventArgs) => Unit) {
subscribers += key -> e;
}
}
The get method of a Map gives you an Option of the value, not the value. Thus, if the key if found in the map, you get Some(value), if not, you get None. So you need to first "unroll" that option to make sure there is actually a value of a function which you can invoke (call apply on):
def trigger(e: Event): Unit =
subscribers.get(e.key).foreach(_.apply(e.EventArgs))
or
def trigger(e: Event): Unit =
subscribers.get(e.key) match {
case Some(value) => value(e.EventArgs)
case None =>
}
There are many posts around explaining Scala's Option type. For example this one or this one.
Also note Luigi's remark about using an immutable map (the default Map) with a var instead.
Since the get method returns Option, you can use 'map' on that:
subscribers.get(e.key).map(f => f(e.EventArgs))
or even shorter:
subscribers.get(e.key) map (_(e.EventArgs))
get only takes one argument. So subscribers.get(e.key) returns an Option, and you're trying to feed (e.EventArgs) to that Option's apply method (which doesn't exist).
Also, try making the subscribers a var (or choosing a mutable collection type). At the moment you have an immutable collection and an immutable variable, so your map cannot change. A more idiomatic way to declare it would be
var subscribers = Map[String, EventArgs => Unit]()
HashMap.get() in Scala works in a bit different way, than in Java. Instead of returning value itself, get() returns Option. Option is a special type, that can have 2 values - Some(x) and None. In first case it tells "there's some value with such a key in a map". In second case it tells "nope, there's nothing (none) for this key in a map". This is done to force programmers check whether map actually has an object or not and avoid NullPointerException, which appears so frequently in Java code.
So you need something like this:
def trigger(e: Event) {
val value = subscribers.get(e.key)
value match {
case None => throw new Exception("Oops, no such subscriber...")
case Some(f) => f(e.EventArgs)
}
}
You can find more info about Option type and pattern matching in Scala here.