I'm wondering if it's possible to auto update the User's column('number of posts') if the Posts table updates. The Post entity has a ManyToOne relation with User('userId'). Is there a way to make the User Table "listen" to the Post Table and automatically updates the number of post column, or i need to write it in the post service create function to do so. I'm new to sql so i'm just trying new stuff. I'm using NestJS,typeORM, Postgres and Graphql
#Kendle's answer does work and has the advantage of pushing the computation and complexity down onto your DB server. Alternatively, you can keep that logic in the application by leveraging TypeORM's Subscribers functionality. Documentation can be found here.
In your specific use case, you could register a subscriber for your Post entity implementing afterInsert and afterRemove (or afterSoftRemove if you soft delete posts) to increment and the decrement the counter respectively.
You don't want to duplicate that data. That's the whole idea of a relational database that different data is kept in different tables.
You can create a view if you want to avoid typing a query with a JOIN each time.
For example you might create the view below:
CREATE VIEW userPosts AS
SELECT
user.id,
user.name,
COUNT(posts.id)
FROM users
LEFT JOIN posts ON user.id = posts.user_id
ORDER BY user.id;
Once you have created the view your can query it as if it were a table.
SELECT * FROM userDate WHERE id = '0001';
Of course I don't have your table definitions and data so you will need to adapt this code to your tables.
Related
I am new to the NoSql world. I am building a serverless app with dynamodb. In a relational DB when I would have 3 entities like post, post_likes and post_tags I would have few tables and use joins to fetch data. But, I wonder how should one make a NoSql structure for a scenario where post has one to many relationship with likes, and many to many with tags.
Post model:
user_id <string>
attachment_url <string>
description <string>
public <boolean>
Like model:
user_id <string>
post_id <string>
type <string>
Tag model:
name <string>
I have few access patterns:
Get all public posts
Get all posts filtered by a single tag and public status
Get all posts by user id
Get a single post by post id
And each time a post should be fetched with tags data, and likes data including user data that is attached to a like.
In relational DB I would create post_tags table and fetch all post by tags. But, how can I do this with dynamodb?
I am struggling to figure out how my table should look like and what to set as primary and sort keys amongst post_id, user_id, tag_name or public fields for this case?
My initial thought was to build a table with entity that would look like this:
Partition key | Sort key | data attributes
tag_name | post_id | public | user_id | likes[] | other post attributes...
Then this table would look something like this:
I have set the 2 Global secondary indexes.
First Global secondary index:
partition key set to public and sort key to post_id
Second Global secondary index:
partition key set to user_id and sort key to post_id
That way for each tag a post has, I would have a duplicate of that post in the table. I thought by having a tag as a first filter, that way I could query efficiently posts if I need to query them by a tag.
But, if I do a query by just a public status or user_id, I would get all the duplicates of posts for each tag they belong to.
Or should I have 3 separate entities in the table, tags, posts and likes and if I fetch a post by a tag, I would first do one query to find all post_ids by a tag, then do the second query to fetch posts and their likes id, and then do the third query to fetch the likes array.
I don't know what is the best practice when it comes to this things, since I only just started using dynamodb.
How should this DB structure look like then?
You're off to a great start by thinking deeply about your access patterns and defining your entities (Posts, Users, Likes, etc). As you know, having a thorough understanding of your access patterns is critical to storing your data in DynamoDB.
While reviewing my answer, keep in mind that this is only one solution. DynamoDB gives you a ton of flexibility when defining your data model, which can be both a blessing and a curse! This answer is not meant to be the way to model these access patterns. Instead, it's one way that these access patterns can be implemented. Let's get into it!
I like to start by listing the entities we need to model, as well as the Primary key for each. Throughout this post, I'll be using composite primary keys, which are keys made up of a Partition Key (PK) and a Sort Key (SK). Let's start out with a blank table and fill it out as we go.
Partition Key Sort Key
User
Post
Tag
Users
Users are central to your application, so I'll start there.
Let's start by defining a User model that lets us identify a User by ID. I'll use the pattern USER#<user_id> for the PK and SK of the User entity.
This supports the following access patterns (examples in pseudocode for simplicity):
Fetch User by ID
ddbClient.query(PK = USER#1, SK = USER#1)
I'll update the table with the new PK/SK pattern for Users
Partition Key Sort Key
User USER#<user_id> USER#<user_id>
Post
Tag
Posts
I'll start modeling Posts by focusing on the one-to-many relationship between Users and their Posts.
You have an access pattern to fetch All Posts by UserId, so I'll start by adding the Post model to the User partition. I'll do this by defining a PK of USER#<user_id> and an SK of POST#<post_id>.
This supports the following access patterns:
Fetch User and all Posts
ddbClient.query(PK = USER#<user_id>)
Fetch User Posts
ddbClient.query(PK = USER#<user_id>, SK begins_with "POST#")
You may wonder about the odd-looking Post IDs. When fetching Posts, you'll probably want to get the most recent Posts first. You also want to be able to uniquely identify Posts by ID. When you have this sort of requirement, you can use a KSUID as your unique identifier. Explaining KSUID's is a bit out of scope for your question, but know that they are unique and sortable by the time they were created. Since DynamoDB sorts results by the Sort Key, your query for a user's posts will automatically be sorted by creation date!
Updating the PK/SK patterns for your application, we now have
Partition Key Sort Key
User USER#<user_id> USER#<user_id>
Post USER#<user_id> POST#<post_id>
Tag
Tags
We have a few options on how to model the one-to-many relationship between Posts and Tags. You could include a list attribute on your Post item, which simply lists the number of tags on the item. This approach is perfectly fine. However, looking at your other access patterns, I'm going to take a different approach for now (it will be apparent why later).
I will model tags with a PK of POST#<post_id> and an SK of TAG#<tag_name>
Since Primary Keys are unique, modeling tags in this way will ensure that no Post is tagged with the same Tag twice. Additionally, it allows us to have an unbounded number of Tags on a Post.
Updating our PK/SK table for Tag, we have
Partition Key Sort Key
User USER#<user_id> USER#<user_id>
Post USER#<user_id> POST#<post_id>
Tag POST#<post_id> TAG#<tag_name>
At this point we've modeled Users, Posts and Tags. However, we've only addressed one of your four access patterns. Lets see how we can use secondary indexes to support your access patterns.
Note: You could also model Likes in the exact same way.
Defining A Secondary Index
Secondary indexes allow you to support additional access patterns within your data. Let's define a very simple secondary index and see how it supports your various access patterns.
I'm going to create a secondary index that swaps the PK/SK patterns in your base table. This pattern is called an inverted index, and would look like this:
All we've done here is swapped the PK/SK pattern of your base table, which has given us access to two additional access patterns:
Fetch Post by ID
ddbClient.query(IndexName = InvertedIndex, PK = POST#<post_id>)
Fetch Posts by Tag
ddbClient.query(IndexName = InvertedIndex, PK = TAG#<tag_name>)
Fetch All Posts by Public/Private status
You wanted to fetch posts by public/private status, as well as fetching all Posts. One way to fetch all Posts is to put them in a single partition. We can put the public/private status in the sort key to separate the public and private Posts.
To do this, I'll create two new attributes on the Post item: _type and publicPostId. These fields will serve as the PK/SK patterns for the secondary index I'm calling PostByStatus.
After doing this, your base table would look like this:
and your new secondary index would look like this
This secondary index would enable the following access patterns
Fetch All Posts
ddbClient.query(IndexName = PostByStatus, PK = POST)
Fetch All Private Posts
ddbClient.query(IndexName = PostByStatus, PK = POST, SK begins_with "PRIVATE#")
Fetch All Public Posts
ddbClient.query(IndexName = PostByStatus, PK = POST, SK begins_with "PUBLIC#")
Remember, post ID's are KSUID's, so they will naturally be sorted in your results by the date the Post was made.
A Word on Hot Partitions
Storing all your Posts in a single partition will likely result in a hot partition as your application scales. One way to address this is by distributing your Post items across multiple partitions. How you do that is entirely up to you and specific to your application.
One strategy to avoid the single POST partition could involve grouping Posts by creation day/week/month/etc. For example, instead of using POST as your PK in the PostByStatus secondary index, you could use POSTS#<month>-<year> instead, which would look like this:
Your application would need to take this pattern into account when fetching Posts (e.g. start at the current month and go backwards until enough results are fetched), but you'd be spreading the load across multiple partitions.
Wrapping Up
I hope this exercise gives you some ideas on how to model your data to support specific access patterns. Data modeling in DynamoDB takes time to get right, and will likely require multiple iterations to make work for your specific application. It can be a steep learning curve, but the payoff is a solution that brings scale and speed to your application.
I am using go and pq to interface with my postgres database.
I have a simple user table which has basic fields. Id, name, type. My auxillary table, admin inherits from user and adds it's own field panel, and another one that is owner and adds owner. Whether that be using table inheritance, or a supporting table.
My question is if I hit and endpoint that points to user/1 at this point I don't know what type of user this person is yet here. I know we can use jwts and other ways to provide this from the front end. I'm more curious about if there is a way to figure out the user and it's type and query the additional fields in one query?
Ie. I hit the endpoint I would Select from users, get the type, then use that type to get the additional fields. So I would effectively be doing two queries on two tables to get the complete data. Is there a better solution of doing this? Is there some optimizations I could do.
I'm trying to create a simple 2 table database - table 1 holds ClientInfo and table 2 has ClientVisits - Relationship is on ClientInfo.ID->ClientVisits.ClientID. Then I have a form created thus for viewing the ClientInfo plus a child(sub?)table which SHOULD show all the records from ClientVisits where my Form ClientID = ClientVisits.ClientID.
Here is my form
Here is the child table with fields shown
Relationships
So I already have one record in ClientVisits for the currently chosen ClientID form record. But it doesn't show in my Table.ClientVisits. Other than the relationship I don't have any other link between the ClientID and the ClientVisits.ClientID field.
If I need to post further info please let me know, trying to describe this as well as I can - sorry if it's not making sense. Thanks.
You have to link both tables in your form.
In my example, main data of my form is a table called CLIENTES, where it shows all the information about a cliente. It would be exactly the same as your table ClientDetails. In this table, primary key is a field called DNI (it would be the equivalent of your ID field)
I got a second table called CONSULTAS MÉDICAS. This table is just a list of how many times this client comes to see us. It would be the same as your secondary table CLIENT VISITS. In this table, I got a field called PACIENTE, linked to my table CLIENTES. Let me show you.
Ok, now my form is done based on the data of my table CLIENTES, but I got a subform control, where I have linked the table CONSULTAS MÉDICAS
To make this work is pretty easy. Not filters or queries. Just linked child and master fields. To do this, you have to select properties of your subform control, and then go to DATA TAB
Just choose as main field your ID field from table CLIENT DETAILS and link it to child field CLIENT ID from table CLIENT VISITS
That should work for you.
I was wondering with Entity Framework 4.1 code first how do you guys handle queries that involve an existing aspnet_Users table?
Basically I have a requirement for a query that involves the aspnet_Users so that I can return the username:
SELECT t.Prop1, u.Username
FROM Table1 t
INNER JOIN aspnet_User u ON t.UserId = u.UserId
Where t.Prop2 = true
Ideally in linq I would like:
from t in context.Table1
join u in context.aspnet_Users on t.UserId equals u.UserId
where t.Prop2 = true
But I'm not sure how to get aspnet_Users mapping to a class User? how do I make aspnet_Users part of my dbset ?
Any help would be appreciated, thanks in advance
Don't map aspnet_Users table or any other table related to aspnet. These tables have their own data access and their own logic for accessing. Mapping these tables will introduce code duplication, possible problems and breaks separation of concerns. If you need users for queries, create view with only needed information like id, user name, email and map the view. The point is that view will be read only, it will contain only allowed data and your application will not accidentally modify these data without using ASP.NET API.
First read Ladislav's answer. If you still want to go ahead : to do what you want would involve mapping the users and roles and members tables into the codefirst domain - which means writing a membership provider in code-first.
Luckily there is a project for that http://codefirstmembership.codeplex.com/ although its not a perfect implementation. The original is VB, look in the Discussion tab for my work on getting it running in c# MVC.
I'm working with the author on a better implementation that protects the membership data (password, last logged on date, all of the non-allowed data) but allow you to map and extend the user table. But its not ready yet!
You don't really need to use Entity Framework to access aspnet_membership provider accounts. You really just need to create an instance of the membership object, pass in a unique user identifier and a Boolean value indicating whether to update the LastActivityDate value for the user and the method returns a MembershipUser object populated with current values from the data source for the specified user.
You can then access the username by using the property of "Username".
Example:
private MembershipUser user =
Membership.GetUser(7578ec40-9e91-4458-b3d6-0a69dee82c6e, True);
Response.Write(user.UserName);
In case you have additional questions about MembershipProvider, you can read up on it on the MSDN website under the title of "Managing Users by Using Membership".
Hope this helps you some with your requirement.
I'm just starting out with the Entity Framework and ADO.NET Data Services and I've run into an issue that I can't seem to figure out. I have two tables, one that has user information and the other that has a created by field. Within the database, there isn't a foreign key between these tables. The user table contains an arbitrary Id, a username, and a display name. The created by field contains the user's username. In my entity I would like to have the user's display name since this is what I need to display and expose over the ADO.NET Data Service? I'm aware that I could restructure the database, but I was hoping that I could do the join using the username as I would in a SQL statement.
Thanks in advance,
-Damien
You can make a view using a join of both tables, and then use this object to display the user's name.
There's some info on mapping custom queries here.