newly working with GraphQl and wondering is it possible to filter a set in a query? I'm still new to database design as well so could be an issue there.
So I run the below query, managerGwPicks has a field player with is a player object containig their name etc.
This player object contains a set of all the weeks they have played which is a separate table in my database.
So as can be seen in the above image when I display the set it shows all the gameweek data whereas ideally I would like it filtered by the gameweek:21 parameter passed to the managerGwPicks query.
I'm not sure it should be possible as there is no direct link between the managerGwPicks and playergwstats tables but I'd like to be sure that my thinking is correct.
My solution for my front end would be to have two queries, one similar to what I have getting the player information and a second query using the player id and gameweek to query playergwstats to get the player stats for the individual week. Does this sound like a reasonable approach?
It's preferable to avoid query patterns where you have to do multiple back-and-forths between the client and the server. If you can imagine making the link on the client then you can do it directly on the server. If you can go from a managerId and gameweek to a list of players and you can go from players to playergwstats then you can create a join that goes from your two parameters to all the relevant players.
I've covered patterns like this in a series of posts on GraphQL for SQL Developers - look at the join that's used to go from a booking reference to a series of tickets and flights.
Related
I am working with Django and I am a bit lost on how to extract information from models (tables).
I have a table containing different information from various sensors. What I would like to know is if it is possible from the Django models to obtain for each sensor (each sensor has an identifier) the last row of data (using the timestamp column).
In sql it would be something like this, (probably the query is not correct but I think you can understand what I'm trying)
SELECT sensorID,timestamp,sensorField1,sensorField2
FROM sensorTable
GROUP BY sensorID
ORDER BY max(timestamp);
I have seen that the group_by() function exists and also lastest() but I don't get anything coherent and I'm also not clear if I'm choosing the best form.
Can anyone help me get started with this topic? I imagine it is very easy but it is a new world and it is difficult to start.
Greetings!
When you use a PostgreSQL database, you can make use of the .distinct(..) method [Django-doc] of the queryset where you add fields that determine on what these should be distinct.
So you can obtain the latest sensors in Django with:
SensorModel.objects.order_by('sensor', '-timestamp').distinct('sensor')
We thus order by sensor (which is required for a .distinct(..)), and then in case of a tie (so two times the same sensor), we order on the timestamp in descending order, hence we pick the latest SensorModel object for that sensor.
I have 4 tables in my database. The image below shows the rows and columns with the name of the table enclosed in a red box. 4 tables total. Am I going about the relationship design correctly? This is a test project and I am strongly assuming that I will use a JOIN to get the entire set of data on one table. I want to start this very correctly.
A beginner question but is it normal that the publisher table, for example, has 4 rows with Nintendo?
I am using Django 1.7 along with PostgreSQL 9.3. I aim to keep simple with room to grow.
Basically you've got the relations back-to-front here...
You have game_id (i.e. a ForeignKey relation) on each of publisher, developer and platform models... but that means each of those entities can only be related to a single game. I'm pretty sure that's not what you want.
You need it the other way around... instead put three foreign keys onto the game model, one each for publisher, developer and platform.
A ForeignKey is what's called a many-to-one relation. In this example I think what you want is for 'many' games to be related to 'one' publisher. Same for developer and platform.
is it normal that the publisher table, for example, has 4 rows with Nintendo?
No, that's is an example of why you have it backwards. You should only have a single row for each publisher.
yes you are correct in saying that something is wrong.
First of all those screen shots are hard to follow, for this simple example they could work but that is not the right tool, pick up pen and paper and sketch some relational diagrams and think about what are the entities involved in the schema and what are their relations, for example you know you have publishers, and they can publish games, so in this restricted example you have 2 entities, game and publisher, and a relation publish among them (in this case you can place a fk on game if you have a single publisher for a game, or create an intermediary relation for a many to many case). The same point can be made for platform and games, why are you placing an fk to game there, what will happen if the game with id 2 will be published for nintendo 64 ? You are making the exact same mistake in all the entities.
Pick up any book about database design basics, maybe it will help in reasoning about your context and future problems.
I'm building a product with Zend 2 and Doctrine 2 and it requires that I have a separate table for each user to contain data unique to them. I've made an entity that defines what that table looks like but how do I change the name of the table to persist the data to, or in fact retrieve the data from, at run time?
Alternatively am I going to be better off giving each user their own database, and just changing which DB I am connecting to?
I'd question the design-choice at first. What happens if you create a new user after runtime. The table has to be created first? Furthermore, what kind of data are you storing, to me this sounds like a pretty common multi-client capabilities. Like:
tbl_clients
- id
- name
tbl_clientdata
- client_id
- data_1_value
- data_2_value
- data_n_value
If you really want to silo users data, you'd have to go the separate databases route. But that only works if each "user" is really independent of each other. Think very hard about that.
If you're building some kind of software-as-a-service, and user A and user B are just two different customers of yours, with no relationship to each other, then an N+1 database might be appropriate (one db for each of your N users, plus one "meta" database which just holds user accounts (and maybe billing-related stuff).
I've implemented something like this in ZF2/Doctrine2, and it's not terribly bad. You just create a factory for EntityManager that looks up the database information for whatever user is active, and configures the EM to connect to it. The only place it gets a bit tricky is when you find yourself writing some kind of shared job queue, where long-running workers need to switch database connections with some regularity -- but that's doable too.
I need a formula to calculate how much inventory is left on had after a work order has been completed. The work order I am developing is a separate list in sharepoint and I have an inventory list as well.
In the inventory list I have a field called amountinventoried and itemname which the user would put the amount of the item we had on hand during the last manual inventory.
On the work order list I have a field called itemused and amountused I need to find a formula to use on a calculated field in the Inventory list that would go out and simply subtract the amountused from the amountinventoried but only if the itemused and itemname fields matched.
I have been working on this for quite a while and have hit a wall, I'm probably overlooking something extremely easy but I'm still new to sharepoint 2010.
Thanks!
You may be able to do this in a grouped view of the work order list (sort of like this), but I think the design of what you are doing is not suited to using SharePoint lists.
You may be much better off using an SQL database to host and calculate the data and connect it into SharePoint as External Lists using the Business Connectivity Services (brief explanation here).
This gives you the benefit of CRUD functionality in SharePoint, with the extra calculations and trickery available within SQL views and tables.
I am trying to lower the amount of queries that my django app is using, but I am a little confused on how to do it.
I would like to get a query set with one hit to the database and then filter items from that set. I have tried a couple of things, but I always get queries for each set.
let's say I want to get all names from my DB, but also separate out the people just named Ted. Both the names and the ted set will be used in the template.
This will give me two sets, one with all names and one with Ted.. but also hits the database twice:
namelist = People.objects.all()
tedList = namelist.filter(name='ted')
Is there a way to filter the first set without hitting the data base again?
tedList = [person for person in namelist if person.name == 'ted']
This will filter the initial QueryList on the client side.