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.
Related
What I want is that when I have looked up a user in a table, I want to list all the file urls that the user have access to. My first thought was to have a field in the table with a list of file URLs. However, I have now understood that there are no such field type.
I was then thinking that maybe ForeignKeys might work, but I am having trouble getting my head around it.
Another solution maybe is to have one table for each user, with each row representing each file.
What would you say is best practice in this case?
I am also going to expand into having shared files, but thought that I'd address this issue first.
Suggest you explore the JSON Data Type
2 tables: user and user_uri_permission? 2 columns in the second: userID and URI. When the User-URI pair is in the table the use has access.
I know, there already is similar questions, but I can't find a good answer at my problem.
I'm developing a social network, I have all my users in a table, but each users must be able to save multiple post from the website.
My Question is:
How can I store all the saved post for each user without creating a new table for each users. I know this is bad to do this, so I'm looking for an alternative
If I understand you correctly, you just need a middle table (for example names user_post) that have 2 columns : user_id and post_id
this is a simple implementation of a many-to-many relationship
You only need a table to store all posts call it posts table with structure like this:
|post_id|user_id|title|content|etc..|
So you can do something to save posts and identify them by user_id.
It's called one-to-many relationship, you can search more about database relationships.
I am developing an app with PhoneGap and have been storing the user id and user level in local storage, for example:
window.localStorage["userid"] = "20";
This populates once the user has logged in to the app. This is then used in ajax requests to pull in their information and things related to their account (some of it quite private). The app is also been used in web browser as I am using the exact same code for the web. Is there a way this can be manipulated? For example user changes the value of it in order to get info back that isnt theirs?
If, for example another app in their browser stores the same key "userid" it will overwrite and then they will get someone elses data back in my app.
How can this be prevented?
Before go further attack vectors, storing these kind of sensitive data on client side is not good idea. Use token instead of that because every single data that stored in client side can be spoofed by attackers.
Your considers are right. Possible attack vector could be related to Insecure Direct Object Reference. Let me show one example.
You are storing userID client side which means you can not trust that data anymore.
window.localStorage["userid"] = "20";
Hackers can change that value to anything they want. Probably they will changed it to less value than 20. Because most common use cases shows that 20 is coming from column that configured as auto increment. Which means there should be valid user who have userid is 19, or 18 or less.
Let me assume that your application has a module for getting products by userid. Therefore backend query should be similar like following one.
SELECT * FROM products FROM owner_id = 20
When hackers changed that values to something else. They will managed to get data that belongs to someone else. Also they could have chance to remove/update data that belongs to someone else agains.
Possible malicious attack vectors are really depends on your application and features. As I said before you need to figure this out and do not expose sensitive data like userID.
Using token instead of userID is going solved that possible break attemps. Only things you need to do is create one more columns and named as "token" and use it instead of userid. ( Don't forget to generate long and unpredictable token values )
SELECT * FROM products FROM owner_id = iZB87RVLeWhNYNv7RV213LeWxuwiX7RVLeW12
I'm trying to do it like this:
Every single user can choose fields (like structures on MySQL) where this fields can handle their respective value, it's like doing a DB inside a DB.
But how can I do it using a single table?
(not talking about user accounts etc where I should be able to use a pointer to his own "structure")
Do something like: varchar Key where register something like "Name:asd" where PHP explode : to get the respective structure ('name' in this case) and the respective value? ('asd')
Use BLOB? can someone turn the light on for me? I don't know how to do something where works better than my current explanation...
I know my text is confuse and sorry for any bad english.
EDIT:
Also, they could add multiple keys/"structures" where accepts a new value
And they are not able to see the Database or Tables, they still normal users
My server does not support Postogre
In my opinion you should create two tables.
with the user info
with 3 fields (userid, key and value)
Each user has 1 record in the first table. Each user can have 0 or more records in the second table. This will ensure you can still search the data and that users can easily add more key/value pairs when needed.
Don't start building a database in a database. In this case, since the user makes the field by himself there is no relation between the fields as I understand? In that case it would make sense to take a look at the NoSQL databases since they seem to fit very good for this kind of situations.
Another thing to check is something like:
http://www.postgresql.org/docs/8.4/static/hstore.html
Do not try to build tables like: records, fields, field types etc. That's a bad practice and should not be needed.
For a more specific answer on your wishes we need a bit more info about the data the user is storing.
While i think the rational answer to this question is the one given by PeeHaa, if you really want the data to fit into one table you could try saving a serialized PHP array in one of the fields. Check out serialize and unserialize
Generates a storable representation of a value
This is useful for storing or passing PHP values around without losing
their type and structure.
This method is discouraged as it is not at all scalable.
Use a table with key-value pairs. So three columns:
user id
key ("name")
value ("asd")
Add an index on user id, so that you can query a user's attributes easily. If you wanted to query all users with the same properties, then you could add a second index on key and/or value.
Hope you are using a programming language also to get the data and present them.
You can have a single table which has a varchar field. Then you store the serialized data of the field structure and their value in that field. When you want to get the structure, query the data and De-serialize that varchar field data.
As per my knowledge every programming language supports serialization and De-serialization.
Edited : This is not a scalable option.
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.