I am trying to build a database for my website. There are currently three entries with different attributes in my database. I have not created these entries in order, but I have assigned a 'Chapter number' attribute which indicates the order 1,2,3.
I am now trying to inject this using 'context' and 'render' function in my views. I am using the method 'objects.all()' to add all objects to my context. I have a simple Html file where I am inserting the data from the database by looping over (a simple for loop) these added objects.
Now the output that is being generated (naturally) is that it is following the order in which I created the database. I am not sure how I can have the loop run in such a way that I get these chapters in correct order. Thank you for patiently reading my question. Any help will be appreciated.
You may use the order_by method which is included in Djangos QuerySet API:
https://docs.djangoproject.com/en/3.0/ref/models/querysets/
If you offer some more information of your specific data I might provide you with an example.
For orientation purposes, sorting queried objects by date would work as follows:
most_recent = Entry.objects.order_by('-timestamp')
You can sort by any field like so:
sorted_by_field = Entry.objects.order_by('custom_field')
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’m not sure where to start on this project. I know how to read the contents of the excel spreadsheet, I know how to identify the header row, I know how to loop over the contents. I believe I have the UX portion worked out but I am not sure how to process the data.
I’ve googled and only found .Net solutions but I’m looking for a ColdFusion/Lucee solution.
I have a working form allowing me to map a user's spreasheet column to my database values (this is being kept simple for this post; user does not have direct access to the database).
Now that I have my data, I'm not sure how to loop over the data results. I believe there will be several loops (an outer and an inner). Then of course I also need to loop over the file contents but I think if I can get the headings mapped out,I can figure out the remaining.
Any good links, tutorials, or guides would be greatly appreciated.
Some pseudo code might be enough to get me started.
User uploads form
System reads headers and content.
User is presented form with a list of columns from their uploaded spreadsheet to match with available database fields (eg “column1” matches “customer name”.
User submits form.
Now what?
UPDATED
Here is what the data looks like AFTER the mapping has been done in my form. The column deliiter is the ::: and within the column the ||| indicates the ID associated with the selected column value. I've included the id and the column value since I plan on displaying the mapping again as a confirmation. Having the ID saves a trip to the database.
If I understand correctly, your question is: how do you provide the user a form allowing them to map their spreadsheet columns to that of the database
Since you have their spreadsheet column names, and you have the database column names, then this problem is essentially a UI/UX problem. You need to show both lists, and allow the user to map them. I can imagine several approaches to this. My first thought would be some sort of drag/drop operation, as follows:
Create a list of boxes, one for each field in your database table, and include the field name in (or above) the box. I'll call this the db field list. Then, create another list for each column from the spreadsheet, which I'll call the spreadsheet column list. The user would drag/drop items from the spreadsheet column list to the db field list.
When a mapping has been completed by the user, you would store the column/field names in as data for the DOM element of the db field list box. Then upon submission, you would acquire the mapping data by visiting each box and adding it to an array. Then you would serialize that array into JSON and send that to your form submission handler.
This could be difficult or easy, depending on your knowledge of UI implementations using JavaScript. jQuery makes this easy (if you know jQuery). There's even a jquery UI plugin that does this: https://jqueryui.com/droppable/.
A quick search for javascript drag drop would help, and here's a few articles I found:
https://www.w3schools.com/html/html5_draganddrop.asp
https://medium.com/quick-code/simple-javascript-drag-drop-d044d8c5bed5
You would also need to submit the array of mappings using javascript. You could search for that as well, and here's an article I found:
https://codereview.stackexchange.com/questions/94493/submit-an-array-as-an-html-form-value-using-javascript
Basically, I have a Listing model, where each listing has a country id. I need the country name in my search results view. I know I can do #listing.country.name, but this performs an extra query for each listing in my search results. I'm using Thinking Sphinx, and in my controller I have
#listings = Listing.search(#ts_params).page(page_num).per(limit)
I have tried adding .includes(:countries) and variations thereof but no luck.
What's the best way to go about this? I want the country data to be fetched in the same query as the listings.
I have exactly the same issue with listing images - it is performing an extra query for every listing to find the image, when surely it can be done in one with joins.
Are you trying to eager load the associated model (to avoid an N + 1 query problem), or are you trying to load the associated model into fields on the parent model?
If it's the former, you're probably better off forgetting about :select and instead of :joins using:
ts_params[:sql][:include] = :countries, :listing_images
Now you should be able to call listing.countries and listing.listing_images to access child models, as normal.
Thinking Sphinx provides functionality to eager load associated entities, so for eager loading we don't need to add [:sql]. Following is the way to do this.
For eager loading associated entities using sphinx.
ts_params[:include] = [:country, :listing_image]
I managed to solve this using the :sql hash provided by Thinking Sphinx. I now have the following:
#ts_params[:sql][:joins] = "INNER JOIN countries ON countries.id = listings.country_id INNER JOIN listing_images ON listing_images.listing_id = listings.id"
#ts_params[:sql][:select] = "listings.*, countries.name as country_name, listing_images.image as image_name"
This is correctly retrieving the country name and image name, but I still have a bit of work to do in making it work with the images - I think that will deserve its own question!
Current v4 syntax is:
Article.search :sql => {:include => :user}
Ref: https://freelancing-gods.com/thinking-sphinx/v4/searching.html
I'm listing queryset results and would like to add an option for choosing the order results are displayed.
I would like to pass the actual data from the database to other page for sorting.
I was able to achieve such thing by getting all objects ids and use django session to recreate a new queryset based on the order criteria.
I was thinking if there is any other way to achieve such goal?
10x
Assuming you are currently displaying the data as a table, you could give chance to some javascript client side table sorter such as tablesorter. There are lots of javascript table sorte.
I'm away from my development machine right now, but I think you could just pass the list of ids to a new Queryset, pk__in=list_of_object_ids, and then use the native order_by function.
For example:
objs = Object.objects.filter(pk__in=list_of_object_ids).order_by('value_to_order_by')
Anyway, that's what I would try first, though I'm sure there are better optimizations.
For example, instead of a list of object ids, you could pass a dictionary with a key:value pair that has the value you want to order by.
For example:
[{'obj_id':1,'obj_value':'foo'},{'obj_id':2,'obj_value':'foo'}]
Then use some lambda function to sort it, like here.
I have a model called "Story" that has two integer fields called "views" and "votes". When I retrieve all the Story objects I would like to annotate the returned QuerySet with a "ranking" field that is simply "views"/"votes". Then I would like to sort the QuerySet by "ranking". Something along the lines of...
Story.objects.annotate( ranking=CalcRanking('views','votes') ).sort_by(ranking)
How can I do this in Django? Or should it be done after the QuerySet is retrieved in Python (like creating a list that contains the ranking for each object in the QuerySet)?
Thanks!
PS: In my actual program, the ranking calculation isn't as simple as above and depends on other filters to the initial QuerySet, so I can't store it as another field in the Story model.
In Django, the things you can pass to annotate (and aggregate) must be subclasses of django.db.models.aggregates.Aggregate. You can't just pass arbitrary Python objects to it, since the aggregation/annotation actually happens inside the database (that's the whole point of aggregate and annotate). Note that writing custom aggregations is not supported in Django (there is no documentation for it). All information available on it is this minimal source code: https://code.djangoproject.com/browser/django/trunk/django/db/models/aggregates.py
This means you either have to store the calculations in the database somehow, figure out how the aggregation API works or use raw sql (raw method on the Manager) to do what you do.