I have a structure of data like this on firebase
-B4PWzQ84KUOeuTuxVY:{
doctorId:2,
Message:abc
}
I want to retrieve Message on the basis of StudentId there are so many records
my code only retrieve whole object but i need only Messages values wherever doctorId is 2
db.ref('students/' )
.orderByChild("DoctorId")
.equalTo("2")
.once('value',(whereresult) => {
var message = whereresult.val();
});
There are three problems in the code:
Property names are case sensitive, so doctorId <> DoctorId.
You store the ID as a number, so should pass a number to equalTo.
When you execute a query against the Firebase Database, there will potentially be multiple results. So the snapshot contains a list of those results. Even if there is only a single result, the snapshot will contain a list of one result.
In total:
db.ref('students/' )
.orderByChild("doctorId")
.equalTo(2)
.once('value',(snapshot) => {
snapshot.forEach(function(child) {
console.log(child.key, child.val());
});
});
Related
I have three collections in my Firebase project, one contains locations that users have checked in from, and the other two are intended to hold leaderboards with the cities and suburbs with the most check ins.
However, as a bit of a newbie to NOSQL databases, I'm not quite sure how to do the queries I need to get and set the data I want.
Currently, my checkins collection has this structure:
{ Suburb:,
City:,
Leaderboard:}
The leaderboard entry is a boolean to mark if the check in has already been added to the leaderboard.
What I want to do is query for all results where leaderboard is false, count the entries for all cities, count the entries for all suburbs, then add the city and suburb data to a separate collection, then update the leaderboard boolean to indicate they've been counted.
exports.updateLeaderboard = functions.pubsub.schedule('30 * * * *').onRun(async context => {
db.collection('Bears')
.where('Leaderboard', '==', 'false')
.get()
.then(snap =>{
snap.forEach(x => {
//Count unique cities and return object SELECT cities,COUNT(*) AS `count` FROM Bears GROUP BY cities
})
})
.then(() => {
console.log({result: 'success'});
})
.catch(error => {
console.error(error);
});
})
Unfortunately, I've come to about the limit of my knowledge here and would love some help.
Firebase is meant to be a real-time platform, and most of your business logic is going to be expressed in Functions. Because the ability to query is so limited, lots of problems like this are usually solved with triggers and data denormalization.
For instance, if you want a count of all mentions of a city, then you have to maintain that count at event-time.
// On document create
await firestore()
.collection("city-count")
.doc(doc.city)
.set({
count: firebase.firestore.FieldValue.increment(1),
}, { merge: true });
Since it's a serverless platform, it's built to run a lot of very small, very fast functions like this. Firebase is very bad at doing large computations -- you can quickly run in to mb/minute and doc/minute write limits.
Edit: Here is how Firebase solved this exact problem from the perspective of a SQL trained developer https://www.youtube.com/watch?v=vKqXSZLLnHA
As clarified in this other post from the Community here, Firestore doesn't have a built-in API for counting documents via query. You will need to read the whole collection and load it to a variable and work with the data then, counting how many of them have False as values in their Leaderboard document. While doing this, you can start adding these cities and suburbs to arrays that after, will be written in the database, updating the other two collections.
The below sample code - untested - returns the values from the Database where the Leaderboard is null, increment a count and shows where you need to copy the value of the City and Suburb to the other collections. I basically changed some of the orders of your codes and changed the variables to generic ones, for better understanding, adding a comment of where to add the copy of values to other collections.
...
// Create a reference to the collection of checkin
let checkinRef = db.collection('cities');
// Create a query against the collection
let queryRef = checkinRef.where('Leaderboard', '==', false);
var count = 0;
queryRef.get().
.then(snap =>{
snap.forEach(x => {
//add the cities and suburbs to their collections here and update the counter
count++;
})
})
...
You are very close to the solution, just need now to copy the values from one collection to the others, once you have all of them that have False in leaderboard. You can get some good examples in copying documents from a Collection to another, in this other post from the Community: Cloud Functions: How to copy Firestore Collection to a new document?
Let me know if the information helped you!
I am fetching id column value from database for a particular email. In this case I am passing email and want to get primary key i.e id. This operation is successful as I get object which contains Object with the right and expected result. However I am not able to access the object.
I am receiving object like this:
[ UserInfo { id: 21 } ]
And I am not able to access id part of it.
I am using node.js, postgres for database and typeorm library to connect with database.
const id = await userRepo.find({
select:["id"],
where: {
email:email
}
});
console.log(id)
This prints the above object.
The id I am getting is right. But I am not able to retrieve the id part of the object. I tried various ways for e.g.
id['UserInfo'].id, id.UserInfo.
Please help me in accessing the object I am receiving
Typeorm .find() returns an array of objects containing entries corresponding to your filters, in your case, all entries with an email field corresponding to the email you specified.
Because the result is an array, you can access it this way:
const records = await userRepo.find({
select: ['id'],
where: {
email,
},
})
console.log(records[0].id)
You could also use the .findOne() method, which returns a single element and might be a better solution in your case :)
When you are putting a field in the select part select:["id"], you are only retrieving this part of the database.
It is like your query was this: select id from userRepo where email = email
and you need to put * in the select part to retrieve all the information:
const id = await userRepo.find({
select:["*"],
where: {
email:email
}
});
I am using Cloud Function to send a notification to mobile device. I have two collection in Firestore clientDetail and clientPersonalDetail. I have clientID same in both of the collection but the date is stored in clientDetail and name is stored in clientPersonal.
Take a look:
ClientDetail -- startDate
-- clientID
.......
ClientPersonalDetail -- name
-- clientID
.........
Here is My full Code:
exports.sendDailyNotifications = functions.https.onRequest( (request, response) => {
var getApplicants = getApplicantList();
console.log('getApplicants', getApplicants);
cors(request, response, () => {
admin
.firestore()
.collection("clientDetails")
//.where("clientID", "==", "wOqkjYYz3t7qQzHJ1kgu")
.get()
.then(querySnapshot => {
const promises = [];
querySnapshot.forEach(doc => {
let clientObject = {};
clientObject.clientID = doc.data().clientID;
clientObject.monthlyInstallment = doc.data().monthlyInstallment;
promises.push(clientObject);
});
return Promise.all(promises);
}) //below code for notification
.then(results => {
response.send(results);
results.forEach(user => {
//sendNotification(user);
});
return "";
})
.catch(error => {
console.log(error);
response.status(500).send(error);
});
});
}
);
Above function is showing an object like this
{clienId:xxxxxxxxx, startDate:23/1/2019}
But I need ClientID not name to show in notification so I'll have to join to clientPersonal collection in order to get name using clientID.
What should do ?
How can I create another function which solely return name by passing clientID as argument, and waits until it returns the name .
Can Anybody please Help.?
But I need ClientID not name to show in notification so I'll have to join to clientPersonal collection in order to get name using clientID. What should do ?
Unfortunately, there is no JOIN clause in Firestore. Queries in Firestore are shallow. This means that they only get items from the collection that the query is run against. There is no way to get documents from two top-level collection in a single query. Firestore doesn't support queries across different collections in one go. A single query may only use properties of documents in a single collection.
How can I create another function which solely return name by passing clientID as argument, and waits until it returns the name.
So the most simple solution I can think of is to first query the database to get the clientID. Once you have this id, make another database call (inside the callback), so you can get the corresponding name.
Another solution would be to add the name of the user as a new property under ClientDetail so you can query the database only once. This practice is called denormalization and is a common practice when it comes to Firebase. If you are new to NoQSL databases, I recommend you see this video, Denormalization is normal with the Firebase Database for a better understanding. It is for Firebase realtime database but same rules apply to Cloud Firestore.
Also, when you are duplicating data, there is one thing that need to keep in mind. In the same way you are adding data, you need to maintain it. With other words, if you want to update/detele an item, you need to do it in every place that it exists.
The "easier" solution would probably be the duplication of data. This is quite common in NoSQL world.
More precisely you would add in your documents in the ClientDetail collection the value of the client name.
You can use two extra functions in this occasion to have your code clear. One function that will read all the documents form the collection ClientDetail and instead of getting all the fields, will get only the ClientID. Then call the other function, that will be scanning all the documents in collection ClientPersonalDetail and retrieve only the part with the ClientID. Compare if those two match and then do any operations there if they do so.
You can refer to Get started with Cloud Firestore documentation on how to create, add and load documents from Firestore.
Your package,json should look something like this:
{
"name": "sample-http",
"version": "0.0.1",
"dependencies": {
"firebase-admin": "^6.5.1"
}
}
I have did a little bit of coding myself and here is my example code in GitHub. By deploying this Function, will scan all the documents form one Collection and compare the ClientID from the documents in the other collection. When it will find a match it will log a message otherwise it will log a message of not matching IDs. You can use the idea of how this function operates and use it in your code.
I have been working with the google cloud library, and I can successfully save data in DataStore, specifically from my particle electron device (Used their tutorial here https://docs.particle.io/tutorials/integrations/google-cloud-platform/)
The problem I am now having is retrieving the data again.
I am using this code, but it is not returning anything
function getData(){
var data = [];
const query = datastore.createQuery('ParticleEvent').order('created');
datastore.runQuery(query).then(results => {
const event = results[0];
console.log(results);
event.forEach(data => data.push(data.data));
});
console.log(data)
}
But each time it is returning empty specifically returning this :
[ [], { moreResults: 'NO_MORE_RESULTS', endCursor: 'CgA=' } ]
, and I can't figure out why because I have multiple entities saved in this Datastore.
Thanks
In the tutorial.js from the repo mentioned in the tutorial I see the ParticleEvent entities are created using this data:
var obj = {
gc_pub_sub_id: message.id,
device_id: message.attributes.device_id,
event: message.attributes.event,
data: message.data,
published_at: message.attributes.published_at
}
This means the entities don't have a created property. I suspect that ordering the query by such property name is the reason for which the query doesn't return results. From Datastore Queries (emphasis mine):
The results include all entities that have at least one value for
every property named in the filters and sort orders, and whose
property values meet all the specified filter criteria.
I'd try ordering the query by published_at instead, that appears to be the property with a meaning closest to created.
I am working with NodeJS on Google App Engine with the Datastore database.
Due to the fact that Datastore does not have support the OR operator, I need to run multiple queries and combine the results.
I am planning to run multiple queries and then combine the results into a single array of entity objects. I have a single query working already.
Question: What is a reasonably efficient way to combine two (or more) sets of entities returned by Datastore including de-duplication? I believe this would be a "union" operation in terms of set theory.
Here is the basic query outline that will be run multiple times with some varying filters to achieve the OR conditions required.
//Set requester username
const requester = req.user.userName;
//Create datastore query on Transfer Request kind table
const task_history = datastore.createQuery('Task');
//Set query conditions
task_history.filter('requester', requester);
//Run datastore query
datastore.runQuery(task_history, function(err, entities) {
if(err) {
console.log('Task History JSON unable to return data results. Error message: ', err);
return;
//If query works and returns any entities
} else if (entities[0]) {
//Else if query works but does not return any entities return empty JSON response
res.json(entities); //HOW TO COMBINE (UNION) MULTIPLE SETS OF ENTITIES EFFICIENTLY?
return;
}
});
Here is my original post: Google Datastore filter with OR condition
IMHO the most efficient way would be to use Keys-only queries in the 1st stage, then perform the combination of the keys obtained into a single list (including deduplication), followed by obtaining the entities simply by key lookup. From Projection queries:
Keys-only queries
A keys-only query (which is a type of projection query) returns just
the keys of the result entities instead of the entities themselves, at
lower latency and cost than retrieving entire entities.
It is often more economical to do a keys-only query first, and then
fetch a subset of entities from the results, rather than executing a
general query which may fetch more entities than you actually need.
Here's how to create a keys-only query:
const query = datastore.createQuery()
.select('__key__')
.limit(1);
This method addresses several problems you may encounter when trying to directly combine lists of entities obtained through regular, non-keys-only queries:
you can't de-duplicate properly because you can't tell the difference between different entities with identical values and the same entity appearing in multiply query results
comparing entities by property values can be tricky and is definitely slower/more computing expensive than comparing just entity keys
if you can't process all the results in a single request you're incurring unnecessary datastore costs for reading them without actually using them
it is much simpler to split processing of entities in multiple requests (via task queues, for example) when handling just entity keys
There are some disadvantages as well:
it may be a bit slower because you're going to the datastore twice: once for the keys and once to get the actual entities
you can't take advantage of getting just the properties you need via non-keys-only projection queries
Here is the solution I created based on the advice provided in the accepted answer.
/*History JSON*/
module.exports.treqHistoryJSON = function(req, res) {
if (!req.user) {
req.user = {};
res.json();
return;
}
//Set Requester username
const loggedin_username = req.user.userName;
//Get records matching Requester OR Dataowner
//Google Datastore OR Conditions are not supported
//Workaround separate parallel queries get records matching Requester and Dataowner then combine results
async.parallel({
//Get entity keys matching Requester
requesterKeys: function(callback) {
getKeysOnly('TransferRequest', 'requester_username', loggedin_username, (treqs_by_requester) => {
//Callback pass in response as parameter
callback(null, treqs_by_requester)
});
},
//Get entity keys matching Dataowner
dataownerKeys: function(callback) {
getKeysOnly('TransferRequest', 'dataowner_username', loggedin_username, (treqs_by_dataowner) => {
callback(null, treqs_by_dataowner)
});
}
}, function(err, getEntities) {
if (err) {
console.log('Transfer Request History JSON unable to get entity keys Transfer Request. Error message: ', err);
return;
} else {
//Combine two arrays of entity keys into a single de-duplicated array of entity keys
let entity_keys_union = unionEntityKeys(getEntities.requesterKeys, getEntities.dataownerKeys);
//Get key values from entity key 'symbol' object type
let entity_keys_only = entity_keys_union.map((ent) => {
return ent[datastore.KEY];
});
//Pass in array of entity keys to get full entities
datastore.get(entity_keys_only, function(err, entities) {
if(err) {
console.log('Transfer Request History JSON unable to lookup multiple entities by key for Transfer Request. Error message: ', err);
return;
//If query works and returns any entities
} else {
processEntitiesToDisplay(res, entities);
}
});
}
});
};
/*
* Get keys-only entities by kind and property
* #kind string name of kind
* #property_type string property filtering by in query
* #filter_value string of filter value to match in query
* getEntitiesCallback callback to collect results
*/
function getKeysOnly(kind, property_type, filter_value, getEntitiesCallback) {
//Create datastore query
const keys_query = datastore.createQuery(kind);
//Set query conditions
keys_query.filter(property_type, filter_value);
//Select KEY only
keys_query.select('__key__');
datastore.runQuery(keys_query, function(err, entities) {
if(err) {
console.log('Get Keys Only query unable to return data results. Error message: ', err);
return;
} else {
getEntitiesCallback(entities);
}
});
}
/*
* Union two arrays of entity keys de-duplicate based on ID value
* #arr1 array of entity keys
* #arr2 array of entity keys
*/
function unionEntityKeys(arr1, arr2) {
//Create new array
let arr3 = [];
//For each element in array 1
for(let i in arr1) {
let shared = false;
for (let j in arr2)
//If ID in array 1 is same as array 2 then this is a duplicate
if (arr2[j][datastore.KEY]['id'] == arr1[i][datastore.KEY]['id']) {
shared = true;
break;
}
//If IDs are not the same add element to new array
if(!shared) {
arr3.push(arr1[i])
}
}
//Concat array 2 and new array 3
arr3 = arr3.concat(arr2);
return arr3;
}
I just wanted to write in for folks who stumble upon this...
There is a workaround for some cases of not having the OR operator if you can restructure your data a bit, using Array properties: https://cloud.google.com/datastore/docs/concepts/entities#array_properties
From the documentation:
Array properties can be useful, for instance, when performing queries with equality filters: an entity satisfies the query if any of its values for a property matches the value specified in the filter.
So, if you needed to query for all entities bearing one of multiple potential values, putting all of the possibilities for each entity into an Array property and then indexing it for your query should yield the results you want. (But, you'd need to maintain that additional property, or replace your existing properties with that Array implementation if it could work for all of what you need.)