So I am trying to make a social network on Django. Like any other social network users get the option to like a post, and each of these likes are stored in a model that is different from the model used for posts that show up in the news feed. Now I have tried two choices to get the like status on the go.
1.Least database hits:
Make one sql query and get the like entry for every post id if they exist.Now I use a custom django template tag to see if the like entry for the current post exist in the Queryset by searching an array that contains like statuses of all posts.
This way I use the database to get all values and search for a particular value from the list using python.
2.Separate Database Query for each query:
Here i use the same custom template tag but rather that searching through a Queryset I use the mysql database for most of the heavy lifting.
I use model.objects.get() for each entry.
Which is a more efficient algorithm. Also I was planning on getting another database server, can this change the choice if network latency is only around 0.1 ms.
Is there anyway that I can get these like statuses on the go as boolean values along with all the posts in a single db query.
An example query for the first method can be like
Let post_list be the post QuerySet
models.likes.objects.filter(user=current_user,post__in = post_list)
This is not a direct answer to your question, but I hope it is useful nonetheless.
and each of these likes are stored in a model that is different from the model used for news feed
I think you have a design issue here. It is better if you create a model that describes a post, and then add a field users_that_liked_it as a many-to-many relationship to your user model. Then, you can do something like post.users_that_liked_it and get a query set of all users that liked your page.
In my eyes you should also avoid putting logic in templates as much as possible. They are simply not made for it. Logic belongs into the model class, or, if it is dependent on the page visited, in the view. (As a rule of thumb).
Lastly, if performance is your main worry, you probably shouldn't be using Django anyway. It is just not that fast. What Django gives you is the ability to write clean, concise code. This is much more important for a new project than performance. Ask yourself: How many (personal) projects fail because their performance is bad? And how many fail because the creator gets caught in messy code?
Here is my advice: Favor clarity over performance. Especially in a young project.
Related
How to generate MySQL Querys with LUIS and fetch data from the DB hosted in Azure?
Should generate a natural language query to an MySQL Query.
e.g.
How much beer was drunken on the oktoberfest 2018?
--> GET amountOfBeer FROM Oktoberfest WHERE Year ==2018;
Does anyone has an idea how to get this to work?
Already generated small Intents in LUIS e.g. GetAmountOfBeer
Dont know how to generate the MySQL Statements and how to get the data from the DB.
Thanks.
You should be able to achieve this, or something similar, using intents and entities. How successful this can be depends on how many and how diverse your queries need to be. First lets start with the phrase you mentioned: "How much beer was drunken on the oktoberfest 2018". You can easily (as you've done) add this as an utterance for an intent, GetAmountOfBeer. Though I'm a fan of intent names that you can read as "I want to GetAmountOfBeer", here you may want to name the intent amountOfBeer so you can use it in your query directly.
Next you need to set up you entities. For year (or datetime rather) that should be easy, as I believe there are some predefined entities for this. I think you need to use a datetime recognizer to parse out the right attribute (like year), but I haven't tried to do this before. Next, Oktoberfest seems to be a specific holiday or event in your DB, so you could create a list entity of all the events you have.
What you are left with is something like (pseudocode) GET topIntent FROM eventEntity WHERE Year ==datetime.Year, or something like that.
If your query set is more complex, you might have to have multiple GET statements, but you could put those in a switch statement by topIntent so that, no matter what the intent is, you can parse out the correct values. You also might want to build this into a dialog where you can check if the entities exist, and if not, you can prompt the user for the missing data.
In my Firebase database, I have a data structure similar to this:
The post ID (1a3b3c4d5e) is generated by the ChildByAutoId() function.
The user ID (fn394nf9u3) is the UID of the user.
In my app, I have a UILabel (author) and I would like to update it with the 'full name' of the user who created the post.
Since I have a reference to the post ID in the users part of the database, I assume there must be some code (if statement?) to check if the value exists and if so, update the label.
Can you help with that?
While it is possible to do the query (ref.child("Users").queryOrdered(byChild: "Posts/1a3b3c4d5e").queryEqual(toValue:true)), you will need to have an index on each specific user's posts to allow this query to run efficiently. This is not a feasible strategy.
As usual when working with NoSQL databases: if you need to do something that your current data model doesn't allow, change your data model to allow the use-case.
In this case that can either be adding the UID of the user to each post, or alternative add the user name to each post (as Andre suggests) and determining if/how you deal with user name changes.
Having such relational data in both directions to allow efficient lookups in both directions is very common in NoSQL database such as Firebase and Firestore. In fact I wrote a separate answer about dealing with many-to-many relations.
If you can change the structure then that is very good because I don't think you are maintaining proper structure for database.
You should take one more key name createdBy inside the Post node so actully structure would be
{description:"Thus the post is here", title:"Hello User", createdBy:"Javed Multani"}
Once you do this, It will dam easy to get detail of user.
OR
Unethical solution,
You can achieve this thing like while you are going to show Post from post node of firabase. Definitely you'll get the auto generated postid like:
1a3b3c4d5e
now first you should first get only posts then inside the successfully getting data and parsing you have to get users and find inside the user by putting the codition like postId == UserPostId if match found take fullname value from there.
as my first Rails app, I am building a homework management app which has these tables:
users (from Devise authentication)
schools
courses
assignments
Unlike most examples of course/grading apps I've found, this one is never concerned with all the grades for all students for a particular course, but has only a 1:many relationship between student and courses. So the examples don't really help me.
In order to calculate a user's current grade in any given course (which requires access to data in both course model and assignment model), I am following a suggestion from here on Stack Overflow and creating a PORO in the app/models directory called GradeCalculator.
But this is my first experience with building a PORO into a Rails app, and most of the documentation I'm finding online is for more sophisticated users. I'm assuming it doesn't need a controller (please correct me if I'm wrong), and I see that building it is as simple as:
app/models/gradecalculator.rb
Class GradeCalculator
def calculate_current_course_grade(course_id)
#graded_course_assignments = Assignment.where(user_id: current_user.id, course_id: course_id, graded: true)
#grab weights for each type of assignment in #graded_course_assignments from courses table
#do some calculations
#return the array
end
def calculate_user_GPA(current_user.id)
#more of the same
end
end
My questions are:
Can a PORO access the database (to get data from the courses and assignments tables). Or do I need to pass it all the relevant data from my other classes (like assignments) as params when calling it?
1a. If a simple class can access the database, does the syntax differ from that in the models? Would the above code be able to access Assignment.where?
1b. How would I call this PORO? For example, how would I call it from my views/assignments/index.html.erb?
Can it access Devise's current_user helper?
Tangentially, I just realized that I could store assignment weights in the assigments table. I was thinking chronologically (user inputs number of homework assignments, quizes, etc. at the time of inputting a new course, which determines the weight for each type of assignment), but I could programmatically have each new assignment populate its own weight field by referencing the number of like assignments from its parent course. This would mean, logically, I could do the grade calculation right in the Assignment model. But if extra credit or other changes were added to the course, all the assignments might then have to recalculate their weights. Which way is more correct?
Writing these questions makes me suspect that I am just to pass my PORO the relevant data from my view, let it do calculations on that data and return a grade. But I will post anyway, just in case I'm wrong.
The reason for breaking business logic out into POROs like this is usually to make your code easier to reason about and easier (and faster) to test. To that end, you do not want GradeCalculator to know or care how Assignment works. You should just pass GradeCalculator all of the data it needs (or a Relation, which quacks like an Enumerable). Having GradeCalculator call Assignment.where means that your tests will depend on ActiveRecord, and the database, which means they'll be slow. If GradeCalculator just expects an array, in your tests you'll just have to mock an array of objects that respond to whatever attribute methods GradeCalculator needs to know about, and you'll be able to run them without loading Rails at all. (It's common to have a separate spec_helper.rb and rails_helper.rb so that specs that don't need Rails can run without loading Rails, which makes them so much faster.)
Per your second question my advice is similar: Decouple your POROs as much as possible from Rails and from Devise.
I need to sort activerecord data by facebook likes. I assume this means that I will need to add a likes field to my model and then populate this with the number of likes that objects related page has had.
Just wondering if there is a better way to do this and how I would go about populating the likes column in the db with the number of likes. Just looking for the best method to do this really.
My current idea is to create the likes field and try and populate it from json object returned from facebookgraph so I can use the activerecord order method to sort. Just not sure if this is the best way and the best way to get the data into the db.
Any help would be much appreciated.
There doesn't seem to be anything wrong with what you are suggesting, but you should bear in mind that storing the number of likes in a model is going to require you to update that frequently with the number of likes from the Facebook Graph API (which is what I assume that you are using).
It might be better to not store the number of likes directly in your application, but simply pull them when your app needs them - this way you will know they are up-to-date, and a post hasn't been liked/unliked since you last polled.
I am trying to understand the concept of document storage and fail to see how it would apply to some situations. For example, in the case of a CMS/blog engine there may be data in the form of:
Posts
Categories
Users
Comments
In something such as MySQL one might have a table for each, then a join table for each set of related data. i.e. posts_table, categories_table, categories_posts_table
In this case, posts_table would contain the post data, categories_table would contain the categories data and categories_posts_table would contain 2 foreign keys used to associate a specific category to a specific post.
How does this translate into something like mongodb?
The only way i can see this setup being structured in mongo is something like:
posts_collection
The output of a single bson document might look similar to:
{
"title" : "title",
"body" : "blah body",
"categories" : [
"category1",
"category2"
]
}
That makes sense, but it seems like categories are going to be duplicated all over the place. With out some sort of relation, you could never be able to simply change the category name and have it reflected across all of your blog posts (?).
Additionally what if these were like binary documents that took up a lot of space? Instead of duplicating the same image over and over it seems like a relationship would work better?
I guess this is a pretty open question, but i was looking for anyone's input on how i should mentally take apart a problem to tell if it should fit in a db like mongo or not. And equally important is how does one structure data correctly?
I have not touched on Users but it seems like EVERYTHING in this would ultimately end up as an embedded document inside of a User's collection since the User kind of starts everything.
thanks a lot.
What's interesting about document databases is that you really need to think about how your data is going to be used. Storing the same information in multiple places (denormalization) is fine in a document database. So you're correct when you say you could have a root User document with everything else embedded in it.
From my limited experience, there's not a "right" way to model a particular set of data, it's more about how that data is going to be used in the future.
It IS possible to reference another documents. For example if you want a Posts collection and have each Post reference a User document in the Users collection. Take a look at this article about Embed vs. Reference.