I'm new to graphdb and Neo4J, so I thougt it would be a great start to buy their new graph db book, but has been very disappointed as I can't even follow along in the book.
The problem is that I don't understand the indexing, how it works and they don't even explain, like for example this code:
CREATE (alice {username: 'Alice'}), (bob {username: 'Bob'}), (charlie {username: 'Charlie'}),
(davina {username: 'Davina'}), (edward {username: 'Edward'}), (alice)-[:ALIAS_OF]->(bob);
And when I type in this:
START bob=node:user(username='bob'), charlie=node:user(username='Charlie'), davina=node:user(username='Davina'), edward=node:user(username='Edward')
CREATE(bob)-[:EMAILED]->(charlie), (bob)-[:CC]->(davina),(bob)-[:BCC]->(edward)
I get following error: ==> MissingIndexException: Index user does not exist
Could someone please explain to me how I index the "user".
Neo4j uses a inverted index powered by Lucene by default. So knowing it would help you understand better. I wrote a blog on this to get you started.
Now, the problem in your query is that you are asking neo4j to search for bob in index user under key username. For this to work you need to either enable auto-indexing or programatically control it.
Related
I tried to search for an example but, I presume it's not doable. I am looking to hopefully be proven wrong or to find an official confirmation that it's not doable.
Before using Hasura, I was doing transactional SQL queries that ensured that data was kept consistent.
For example, I would like to create a password reset token if a user requests it, only if the user can be found using an email address. Right now, I have to do 2 queries:
Try to find a user with the specified email address
Insert and assign the token to this user id
In that case, it's not too bad, but now if I want to consume that token, I have to do 3 queries:
Find the valid token
Change the password to the user associated with that token
Delete the token
Obviously, if something goes wrong and the token is not deleted, this could be an issue - so I would be curious to see if there would be ways to merge these queries/mutations into transactions.
Sounds like supporting nested updates would solve this problem for you with the least amount of effort. We are working on a rfc for the feature and hope to start development soon. Please follow this Github issue on our community for future updates.
https://github.com/hasura/graphql-engine/issues/1573
This comment outlines the current scope of the proposed feature. The rfc will provide a more complete explanation.
https://github.com/hasura/graphql-engine/issues/1573#issuecomment-1338057350
You can apply changes to rows that you filter by certain criteria. Here is a sample mutation:
mutation PasswordUpdate($id: uuid!, $token: String!, $new_password: String!) {
update_user(
where: {id: {_eq: $id}, token: {_eq: $token}}
_set: {token: null, password: $new_password}
) {
affected_rows
}
}
That query deletes the token and sets a password for all users (hopefully just one) that have the token assigned.
After some research here is what I found:
For the first example:
Try to find a user with the specified email address
Insert and assign the token to this user id
There are no solutions for this today and as answered by #damel, there is an ongoing RFC to support nested mutations: https://github.com/hasura/graphql-engine/issues/1573#issuecomment-1338057350
Hopefully, this feature will be out soon, but in the meantime, for most cases, it's not such a big deal to have multiple queries as it is possible to catch errors on the first query.
For the second example:
Find the valid token
Change the password to the user associated with that token
Delete the token
When sending multiple mutations in the same query, Hasura treats them as a transaction as announced in 2020.
Of course, it would be nice to do this in the same query (similar to the first example) but since there is a transaction on the mutation, for this case it's still not a problem.
I am sure there are probably cases where this can become a problem but I am not exposed to them right now. Nevertheless, it would be great if the RFC makes it to production, giving more options to Hasura users.
I'm new to the noSQL-Thing (I use firebase Realtime-Database for starters) and I'm writing a react-js app to manage Meetings and their Agenda Points.
The meeting has some attributes(name, planed duration, Start time, ... ) and the Agendaitems as well (name, planed duration, ... ).
So, my first intuition was to make a class Meeting with a Map of AgendaItems - but the Map doesn't get save in the firebase.
Then I tried a simple array - this works but I read "Arrays are bad in firebase"
So, whats the best strategy here? (I know that is probably a very Basic question)
And, would you put more "advanced" functions in the same Class? - e.g.: "nextAgendaItem", "addAgentaItem" to capsulate these implementation
or would you build a own "HandlerClass" witch has a Meeting as member
Whenever I encounter code snippets on the web, I see something like
Meteor.subscribe('posts', 'bob-smith');
The client can then display all posts of "bob-smith".
The subscription returns several documents.
What I need, in contrast, is a single-document subscription in order to show an article's body field. I would like to filter by (article) id:
Meteor.subscribe('articles', articleId);
But I got suspicious when I searched the web for similar examples: I cannot find even one single-document subscription example.
What is the reason for that? Why does nobody use single-document subscriptions?
Oh but people do!
This is not against any best practice that I know of.
For example, here is a code sample from the github repository of Telescope where you can see a publication for retrieving a single user based on his or her id.
Here is another one for retrieving a single post, and here is the subscription for it.
It is actually sane to subscribe only to the data that you need at a given moment in your app. If you are writing a single post page, you should make a single post publication/subscription for it, such as:
Meteor.publish('singleArticle', function (articleId) {
return Articles.find({_id: articleId});
});
// Then, from an iron-router route for example:
Meteor.subscribe('singleArticle', this.params.articleId);
A common pattern that uses a single document subscription is a parameterized route, ex: /posts/:_id - you'll see these in many iron:router answers here.
I want to build a realtime quiz game which randomly matches two players (according to their winning rate if they are logged in). I've read through the book Discover Meteor and have a basic understanding of the framework, but I just have no idea of how to implement the matching part. Anyone know how to do that?
if you want to match users who have scores close to each other, you can do something like this : mongodb - Find document with closest integer value
The Meteor code for those Mongo queries is very similar, but there are some subtle differences that are kind of tricky. In Meteor, it would look something like this :
SP // "selected player" = the User you want to match someone up with
var score = SP.score; // selected player's score
var queryLow = {score: {$lte:score},_id:{$ne:SP._id}};
var queryHigh = {score:{$gte:score},_id:{$ne:SP._id}};
// "L" is the player with the closest lower score
var L=Players.findOne(queryLow,{sort:{score:-1},limit:1});
// "H" is the player with the closest higher score
var H=Players.findOne(queryHigh,{sort:{score:1},limit:1});
so, now you have references to the players with scores right above and right below the 'selected player'. In terms of making it random, perhaps start with a simple algorithm like "match me with the next available player who's score is closest" , then if it's too predictable and boring you can throw some randomness into the algorithm.
you can view the above Meteor code working live here http://meteorpad.com/pad/4umMP4iY8AkB9ct2d/ClosestScore
and you can Fork it and mess about with the queries to see how it works.
good luck! Meteor is great, I really like it.
If you add the package peppelg:random-opponent-matcher to your application, you can match together opponents like this:
On the server, you need to have an instance of RandomOpponentMatcher like this:
new RandomOpponentMatcher('my-matcher', {name: 'fifo'}, function(user1, user2){
// Create the match/game they should play.
})
The function you pass to RandomOpponentMatcher will get called when two users been matched to play against each other. In it, you'll probably want to create the match the users should play against each other (this package does only match opponents together, it does not contain any functionality for playing games/matches).
On the client, you need to create an instance of RandomOpponentMatcher as well, but you only pass the name to it (the same name as you used on the server):
myMatcher = new RandomOpponentMatcher('my-matcher')
Then when the users is logged in and which to be matched with a random opponent, all you need to do is to call the add method. For example:
<template name="myTemplate">
<button class="clickMatchesWithOpponent">Match me with someone!</button>
</template>
Template.myTemplate.events({
'click .clickMatchesWithOpponent': function(event, template){
myMatcher.add()
}
})
When two different logged in users has clicked on the button, the function you passed to RandomOpponentMatcher on the server will get called.
One implementation might be as follows:
A user somehow triggers a 'looking for game' event that sets an attribute on user.profile.lookingForGame to true. The event then makes a call to a server side Meteor method which queries for all other online users looking for games.
From there you it really depends on how you want to handle users once they 'match'.
To determine all online users, try using the User Status package:
https://github.com/mizzao/meteor-user-status
Once added, any online user will have an attribute in the profile object of 'online'. You can use this to query for all online users.
I'm trying to use the cfs:http-publish package at https://github.com/CollectionFS/Meteor-http-publish. While I've got the GET - /api/list functionality working, I don't know how to obtain a single document:
(GET - /api/list/:id - find one published document).
Can someone provide a curl example of this, assuming a certain collection of objections.
eg: {a:3, b:2}, {a:4, b:3}, and requiring to obtain the object with {a:3}.
Thanks.
You need to put it in the query function.
HTTP.publish({collection: myList},function( ){
return myList.find(this.query);
});
this.query contains the data you sent with your request.
curl http://localhost:3000/api/myList?a=3
I don't know enough about mongo to know if this is a potential security risk, if anyone can comment on that please do.