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• implementing dynamic query handler on historical data

  - by user2390183

  EDIT : Refined question to focus on the core issue Context: I have historical data about property (house) sales collected from various sources in a centralized/cloud data source (assume info collection is handled by a third party) Planning to develop an application to query and retrieve data from this centralized data source Example Queries: Simple : for given XYZ post code, what is average house price for 3 bed room house? Complex: What is estimated price for an house at "DD,Some Street,XYZ Post Code" (worked out from average values of historic data filtered by various characteristics of the house: house post code, no of bed rooms, total area, and other deeper insights like house building type, year of built, features)? In addition to average price, the application should support other property info ** maximum, or minimum price..etc and trend (graph) on a selected property attribute over a period of time**. Hence, the queries should not enforce the search based on a primary key or few fixed fields In other words, queries can be What is the change in 3 Bed Room house price (irrespective of location) over last 30 days? What kind of properties we can get for X price (irrespective of location or house type) The challenge I have is identifying the domain (BI/ Data Analytical or DB Design or DB Query Interface or DW related or something else) this problem (dynamic query on historic data) belong to, so that I can do further exploration My findings so far I could be wrong on the following, so please correct me if you think so I briefly read about BI/Data Analytics - I think it is heavy weight solution for my problem and has scalability issues. DB Design - As I understand RDBMS works well if you know Data model at design time. I am expecting attributes about property or other entity (user) that am going to bring in, would evolve quickly. hence maintenance would be an issue. As I am going to have multiple users executing query at same time, performance would be a bottleneck Other options like Graph DB (http://www.tinkerpop.com/) seems to be bit complex (they are good. but using those tools meant for generic purpose, make me think like assembly programming to solve my problem ) BigData related solution are to analyse data from multiple unrelated domains So, Any suggestion on the space this problem fit in ? (Especially if you have design/implementation experience of back-end for property listing or similar portals)

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• Most common parts of a SELECT SQL query?

  - by jnrbsn

  I'm writing a function that generates a SELECT SQL query. (I'm not looking for a tool that already does this.) My function currently takes the following arguments which correspond to different parts of the SELECT query (the base table name is already known): where order fields joins group limit All of these arguments will be optional so that the function generates something like this by default: SELECT * FROM `table_name` I want to order the arguments so that the most often used parts of a SELECT query are first. That way the average call to the function will use as few of the arguments as possible rather than passing a null value or something like that to skip an argument. For example, if someone wanted to use the 1st and 3rd arguments but not the rest, they might have to pass a null value as the 2nd argument in order to skip it. So, for general purpose use, how should I order the arguments? Edit: To be more precise, out of the query parts I listed above, what is the order from most used to least used? Also, I'm not looking for solutions that allow me to not have to specify the order. Edit #2: The "fields" argument will default to "*" (i.e all fields/columns).

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• How to do left joins with least-n-per-group query?

  - by Nate

  I'm trying to get a somewhat complicated query working and am not having any luck whatsoever. Suppose I have the following tables: cart_items: +--------------------------------------------+ | item_id | cart_id | movie_name | quantity | +--------------------------------------------+ | 0 | 0 | braveheart | 4 | | 1 | 0 | braveheart | 9 | | . | . | . | . | | . | . | . | . | | . | . | . | . | | . | . | . | . | +--------------------------------------------+ movies: +------------------------------+ | movie_id | movie_name | ... | +------------------------------+ | 0 | braveheart | . | | . | . | . | | . | . | . | | . | . | . | | . | . | . | +------------------------------+ pricing: +-----------------------------------------+ | id | movie_name | quantity | price_per | +-----------------------------------------+ | 0 | braveheart | 1 | 1.99 | | 1 | braveheart | 2 | 1.50 | | 2 | braveheart | 4 | 1.25 | | 3 | braveheart | 8 | 1.00 | | . | . | . | . | | . | . | . | . | | . | . | . | . | | . | . | . | . | | . | . | . | . | +-----------------------------------------+ I need to join the data from the tables, but with the added complexity that I need to get appropriate price_per from the pricing table. Only one price should be returned for each cart_item, and that should be the lowest price from the pricing table where the quantity for the cart item is at least the quantity in the pricing table. So, the query should return for each item in cart_items the following: +---------------------------------------------+ | item_id | movie_name | quantity | price_per | +---------------------------------------------+ Example 1: Variable passed to the query: cart_id = 0. Return: +---------------------------------------------+ | item_id | movie_name | quantity | price_per | +---------------------------------------------+ | 0 | braveheart | 4 | 1.25 | | 1 | braveheart | 9 | 1.00 | +---------------------------------------------+ Note that this is a minimalist example and that additional data will be pulled from the tables mentioned (particularly the movies table). How could this query be composed? I have tried using left joins and subqueries, but the difficult part is getting the price and nothing I have tried has worked. Thanks for your help. EDIT: I think this is similar to what I have working with my "real" tables: SELECT t1.item_id, t2.movie_name, t1.quantity FROM cart_items t1 LEFT JOIN movies t2 ON t2.movie_name = t1.movie_name WHERE t1.cart_id = 0 Assuming I wrote that correctly (I quickly tried to "port over" my real query), then the output would currently be: +---------------------------------+ | item_id | movie_name | quantity | +---------------------------------+ | 0 | braveheart | 4 | | 1 | braveheart | 9 | +---------------------------------+ The trouble I'm having is joining the price at a certain quantity for a movie. I simply cannot figure out how to do it.

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• How can I remove this query from within a loop?

  - by Chris

  I am currently designing a forum as a personal project. One of the recurring issues I've come across is database queries in loops. I've managed to avoid doing that so far by using table joins or caching of data in arrays for later use. Right now though I've come across a situation where I'm not sure how I can write the code in such a way that I can use either of those methods easily. However I'd still prefer to do at most 2 queries for this operation rather than 1 + 1 per group of forums, which so far has resulted in 5 per page. So while 5 isn't a huge number (though it will increase for each forum group I add) it's the principle that's important to me here, I do NOT want to write queries in loops What I'm doing is displaying forum index groupings (eg admin forums, user forums etc) and then each forum within that group on a single page index, it's the combination of both in one page that's causing me issue. If it had just been a single group per page, I'd use a table join and problem solved. But if I use a table join here, although I can potentially get all the data I need it'll be in one mass of results and it needs displaying properly. Here's the code (I've removed some of the html for clarity) <?php $sql= "select * from forum_groups"; //query 1 $result1 = $database->query($sql); while($group = mysql_fetch_assoc($result1)) //first loop {?> <table class="threads"> <tr> <td class="forumgroupheader"> <?php echo $group['group_name']; ?> </td> </tr> <tr> <td class="forumgroupheader2"> <?php echo $group['group_desc']; ?> </td> </tr> </table> <table> <tr> <th class="thforum"> Forum Name</th> <th class="thforum"> Forum Decsription</th> <th class="thforum"> Last Post </th> <tr> <?php $group_id = $group['id']; $sql = "SELECT forums.id, forums.forum_group_id, forums.forum_name, forums.forum_desc, forums.visible_rank, forums.locked, forums.lock_rank, forums.topics, forums.posts, forums.last_post, forums.last_post_id, users.username FROM forums LEFT JOIN users on forums.last_post_id=users.id WHERE forum_group_id='{$group_id}'"; //query 2 $result2 = $database->query($sql); while($forum = mysql_fetch_assoc($result2)) //second loop {?> So how can I either a) write the SQL in such a way as to remove the second query from inside the loop or b) combine the results in an array either way I need to be able to access the data as an when so I can format it properly for the page output, ie within the loops still.

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• In Django, can you add a method to querysets?

  - by Paul D. Waite

  In Django, if I have a model class, e.g. from django.db import models class Transaction(models.Model): ... then if I want to add methods to the model, to store reasonably complex filters, I can add a custom model manager, e.g. class TransactionManager(models.Manager): def reasonable_complex_filter(self): return self.get_query_set().filter(...) class Transaction(models.Model): objects = TransactionManager() And then I can do: >>> Transaction.objects.reasonably_complex_filter() Is there any way I can add a custom method that can be chained to the end of a query set from the model? I.e. add the custom method in such a way that I can do this: >>> Transaction.objects.filter(...).reasonably_complex_filter()

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• How to create a custom admin configuration panel in Django?

  - by Matteo

  Hi, I would like to create a configuration panel for the homepage of the web-app I'm designing with Django. This configuration panel should let me choose some basic options like highlighting some news, setting a showcase banner, and so on. Basically I don't need an app with different rows, but just a panel page with some configuration options. The automatically generated administration area created by Django doesn't seem to handle this feature as far as I can see, so I'm asking you for some directions. Any hint is highly appreciated. Thank you in advance. Matteo

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• How do I perform a batch insert in Django?

  - by Thierry Lam

  In mysql, you can insert multiple rows to a table in one query for n 0: INSERT INTO tbl_name (a,b,c) VALUES(1,2,3),(4,5,6),(7,8,9), ..., (n-2, n-1, n); Is there a way to achieve the above with Django queryset methods? Here's an example: values = [(1, 2, 3), (4, 5, 6), ...] for value in values: SomeModel.objects.create(first=value[0], second=value[1], third=value[2]) I believe the above is calling an insert query for each iteration of the for loop. I'm looking for a single query, is that possible in Django?

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• How do I do this Database Model in Django?

  - by alex

  Django currently does not support the "Point" datatype in MySQL. That's why I created my own. class PointField(models.Field): def db_type(self): return 'Point' class Tag(models.Model): user = models.ForeignKey(User) utm = PointField() As you can see, this works, and syncdb creates the model fine. However, my current code calculates a length between two Points using raw SQL. cursor.execute("SELECT user_id FROM life_tag WHERE\ (GLength(LineStringFromWKB(LineString(asbinary(utm), asbinary(PointFromWKB(point(%s, %s)))))) < 55)... This says: Select where the length between the given point and the table point is less than 55. How can I do this with Django instead of RAW SQL? I don't want to do cursors and SELECT statements anymore. How can I modify the models.py in order to do this?

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• When I run Django on Dreamhost using SQLite, why do I get an OperationalError telling me that a tabl

  - by Paul D. Waite

  I had a Django site running on Dreamhost. Although I used SQLite when developing locally, I initially used MySQL on Dreamhost, because that’s what the wiki page said to do, and because if I’m using an ORM, I might as well take advantage of it by running against a different database. After a while, I switched the settings on the server to use SQLite, to make it easier to keep my development database in sync with the server one. python manage.py syncdb worked on the server, but when I tried to access the site, I got an OperationalError. The Django error page said that one of my tables didn’t exist. I checked the database using sqlite on the command line on the server, and using python manage.py shell, and both worked fine.

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• IIS URL Rewrite Module Query String Parameters

  - by binarycoder

  Is it possible to use URL Rewrite to provide more complex query string functionality than the "Append query string" checkbox that it has? Specifically, is it possible to specify the keys for certain query string parameters and have it only append those name value pairs. For example, for the input: http://www.example.org/test?alpha=1&beta=2&gamma=3 and the list of query string parameter keys: beta gamma it should output: http://www.example.org/redirect?beta=2&gamma=3 (Note that the query string parameters in the input appear in arbitrary order.)

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• In Django : How to serialize dict object to json ?

  - by Rohit

  I have this very basic problem, >>> serializers.serialize("json", {'a':1}) Traceback (most recent call last): File "<console>", line 1, in <module> File "/usr/lib/pymodules/python2.6/django/core/serializers/__init__.py", line 87, in serialize s.serialize(queryset, **options) File "/usr/lib/pymodules/python2.6/django/core/serializers/base.py", line 40, in serialize for field in obj._meta.local_fields: AttributeError: 'str' object has no attribute '_meta' >>> How can this be done ? Thanks in advance !

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• Django with custom authentication backends, is Csrf middleware really required ?

  - by Hellnar

  Hello, Under Django 1.1.1, I am using several authentication backends such as social-registration for facebook connect and django-emailauth for email based authentication instead of user names. I am curious if the Csrf middleware is an essential security measure as it seems like it sometimes generates problems, especially with facebook connect. My project is rather simple. Each user have a profile which they can fill and a purchase page where they fill the payment for to do purchases. Either of these pages are protected via @login_required.

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• [Django] How to find out whether a model's column is a foreign key?

  - by codethief

  I'm dynamically storing information in the database depending on the request: // table, id and column are provided by the request table_obj = getattr(models, table) record = table_obj.objects.get(pk=id) setattr(record, column, request.POST['value']) The problem is that request.POST['value'] sometimes contains a foreign record's primary key (i.e. an integer) whereas Django expects the column's value to be an object of type ForeignModel: Cannot assign "u'122'": "ModelA.b" must be a "ModelB" instance. Now, is there an elegant way to dynamically check whether b is a column containing foreign keys and what model these keys are linked to? (So that I can load the foreign record by it's primary key and assign it to ModelA?) Or doesn't Django provide information like this to the programmer so I really have to get my hands dirty and use isinstance() on the foreign-key column?

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• Is there any list of blog engines, written in Django?

  - by Big 40wt Svetlyak

  Is there any list of blog engines, written in Django?

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• What's the best way to access Neo4j from Django?

  - by abdel

  it seems that i found something that let me confused; i've found two Neo4j to download to python, the first one is: http://pypi.python.org/pypi/neo4j-embedded and the second one is: https://svn.neo4j.org/components/neo4j.py/trunk/ what's the difference between the two? the first one seems to be big (size), so does this mean that if i use it i'll not need the neo4j community release (milestone)? when i've installed the first one, and tried to test a django example, it seems that the directory named "model" https://svn.neo4j.org/components/neo4j.py/trunk/src/main/python/neo4j/model/ is missing? so what's the difference, and who will be better to use with Django? and what about that one? http://pypi.python.org/pypi/neo4django/

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• Using django-piston, how can I write out HTTP headers in the response?

  - by jimothy4j

  How can I include an HTTP header, such as Cache-Control or Last-Modified, in the response to a django-piston call?

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• Really basic Django E-commerce? Where do I start

  - by Andrew

  I'm trying to set up a really basic e-commerce site with Django, and am trying to figure out the best place to start. I am relatively comfortable with the framework itself, but have never done any sort of e-commerce development in any language, so I want to learn about some best practices so I don't make any huge or obvious mistakes. I've looked at Satchmo, and even went as far as installing and playing around with it, but it looks like way more than I want. I basically want to show users a list of things, and let them click a button to buy one. No cart, no shipping, just click a button, connect with Authorize.net (or something similar) to do the transaction, and then display a confirmation page. Any suggestions or online tutorials people have found helpful? Even perhaps a tutorial in another language. Or maybe a really lightweight Django plugin that doesn't try to do everything like Satchmo? I've been coming up with very little so far. Thanks!

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• Avoid 404 page override

  - by vernomcrp

  I 'm using django-lfs with default django-app.Its appear django-lfs override 404 default template. How to avoid this process

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• How do I construct a Django form with model objects in a Select widget?

  - by Thierry Lam

  Let's say I'm using the Django Site model: class Site(models.Model): name = models.CharField(max_length=50) My Site values are (key, value): 1. Stackoverflow 2. Serverfault 3. Superuser I want to construct a form with an html select widget with the above values: <select> <option value="1">Stackoverflow</option> <option value="2">Serverfault</option> <option value="3">Superuser</option> </select> I'm thinking of starting with the following code but it's incomplete: class SiteForm(forms.Form): site = forms.IntegerField(widget=forms.Select()) Any ideas how I can achieve that with Django form?

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• Turbogears 2 vs Django - any advice on choosing replacement for Turbogears 1?

  - by michela

  I have been using Turbogears 1 for prototyping small sites for the last couple of years and it is getting a little long in the tooth. Any suggestions on making the call between upgrading to Turbogears 2 or switching to something like Django? I'm torn between the familiarity of the TG community who are pretty responsive and do pretty good documentation vs the far larger community using Django. I am quite tempted by the built-in CMS features and the Google AppEngine support. Any advice? Thanks .M.

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• Is it possible to use Django's testing framework without having CREATE DATABASE rights?

  - by superjoe30

  Since I don't have a hundred bazillion dollars, my Django app lives on a shared host, where all kinds of crazy rules are in effect. Fortunately, they gave me shell access, which has allowed me to kick butts and take names. However I can't do anything about not having CREATE DATABASE rights. I'm using postgresql and have a killer test suite, but am unable to run it due to the code not being able to create a new database. However I am able to create said database beforehand via cPanel and use it with Django. I just don't have CREATE DATABASE rights. Is there a way I can still run my test suite?

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• pitfalls with mixing storage engines in mysql with django?

  - by Dave Orr

  I'm running a django system over mysql in amazon's cloud, and the database default is innodb. But now I want to put a fulltext index on a couple of tables for searching, which evidently requires myisam. The obvious solution is to just tell mysql to ALTER TABLE to myisam, but are there going to be any issues with that? One that comes to mind is that I'll have to remember to do that any time I build a new version of the database, which should theoretically be rare, but there doesn't seem to be a way to tell django to please set the storage engine at the table level. I guess I could write a migration (we use south). Any other things I might be missing? What could possibly go wrong?

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• How do I specify (1) an order and (2) a meaninful string representation for users in my Django application?

  - by David Faux

  I have a Django application with users. I have a model called "Course" with a foreign key called "teacher" to the default User model that Django provides: class Course(models.Model): ... teacher = models.ForeignKey(User, related_name='courses_taught') When I create a model form to edit information for individual courses, the possible users for the teacher field appear in this long select menu of user names. These users are ordered by ID, which is of meager use to me. How can I order these users by their last names? change the string representation of the User class to be "Firstname Lastname (username)" instead of "username"?

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• How painful is a django project upload to a live (staging) site?

  - by Ignacio

  Hi, I've getting quite fast with a small django project of mine, which I'm developing locally, of course. But, as I had never worked with django before, I'm not aware of what it implies to upload it and test it on a production server. And I'm quite curious, since I'm very eager to test an early release live. I know there is this document, which I think it'll be really helpful: http://djangobook.com/en/2.0/chapter12/ But, are there any details I should take into account before, during and after the deployment? Any advice or best practices? Thanks.

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• Django: do I need to do HttpResponseRedirect to render a simple string after a POST?

  - by AP257

  I've got a mobile app that makes POST requests to a Django site. I want to return a simple string (not a template-based page) after the app makes the POST request, saying 'Success' or 'Failure' as appropriate. However I know that after a POST request in Django you're supposed to do a HttpResponseRedirect. But, do I really need to redirect to another page and write a new function to handle it, all to output a string? And if so, how do I pass the success/failure status of the app in the HttpResponseRedirect, since it's only supposed to take one argument? Thanks!

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