I can't figure out how to modelise the following situation into a ERD :
A car dealer sells a car to a client.
I suppose there are 3 entities here (without considering the atttributes):
The seller
The client
The car
The relationships are the following (without considering the cardinalities) :
The relationship sell between seller and car represents in the real world that the dealer sell a car
The relationship owns between car and client means in the real wold that a car is owned ny a client
HERE The ERD I have made:
I think that what I have made means A dealer sells a car and a car is owned by a client but I wanted to schematize that A dealer sells a car TO a client and the information meant by the TO is lost in my ERD.
How is the best way to schematize it ?
I know this sounds stupid, but I am not familiar with ERD,
Anyway thanks for your help !
How about a ternary relationship?
Related
The gist of the matter is I want to know the best way to associate the below setup.
I have 2 customer models. Individual Customer & Corporate Customer.
I have another Vehicle model. Which I would like to maintain separately.
I would like to have a HMT model called VehicleOwner. Which now adds the r/ship of any of the two(2) customers as an owner & the vehicle.
The reason for this approach is an architecture design to allow the same vehicle to be migrated to other customers and not have every time a customer wants to add a vehicle; they keep adding a vehicle even if we have it.
My question is this?
How can I link in the Vehicle Owner. That the owner can either be an individual customer or a corporate customer.
Or is there another better way to map the two(2) customers with a vehicle.
Thanks
Perhaps you are looking for Polymorphic association in Rails, in your case it would be, VehicleOwner model should look like
belongs_to :customer, polymorphic: true
In IndividualCustomer and CorporateCustomer models
has_many :vehicle_owners, as: :customer
This is just an example of how to implement this, you can read more about in official Rails guides
https://guides.rubyonrails.org/association_basics.html#polymorphic-associations
Hope that helps!
I have 4 Models, each defined as follows
--Model/Table--
Competition
Matches
Goals
Teams
These 4 models completes a season's worth of soccer league data. The relationship between these tables are already defined. Now, I want to create a class where it picks up data from all 4 models and generate 1, new class. Like so :
class CompetitionSeason < ApplicationRecord
# Use data from all 4 models to construct a soccer season class
end
That is my intention, but I'm not sure if this is the best practice for doing so. It feels... wrong on a Rails framework level. What is the best practice to achieve this?
Thank you.
You should really have another model called Season or some such which owns (has_(one|many)) each of the constituents.
I'm not sure what Competition is.
Match can belong to either a Competition or directly to Season. I don't get what Competition is so I can't make a good recommendation.
Goal should belong to Match or Competition, and not directly to Season. Season can still have many goals through Match or Competition.
Team should have a SeasonTeam junction table.
I am making an app in which there are three models individual, company and event.
company,event and individual lies in a single category.
here the company can create an event where they can choose multiple interests from categories and search for individuals that lies in that categories also when individual signs up they can choose multiple interests from categories table to find the companies of the interests and this same applies for company.
the solution I want is to prepare the best logic for this
my assumption is to create an Interest model where company , event and individuals has_many interests and interest belongs_to category
but this assumption seems to be confusing
Please suggest some logics
I'm trying to model contractor relationships in Neo4J and I'm struggling with how to conceptualize subcontracts. I have nodes for Government Agencies (label: Agency) and Contractors (label:Company). Each of these have geospatial Office nodes with the HAS_OFFICE relationship. I'm thinking of creating a node that represents a Government Contract (label: Contract).
Here's what I'm struggling with: A Contract has a Government Agency (I'm thinking this is a "HAS CONTRACT" relationship) and one or more prime contractor(s) (I'm thinking this is a "PRIME" relationship). Here's where it gets complicated. Each of those primes contractors can have subcontractors under the prime contract only. Graphically, this is:
(Agency) -[HAS_CONTRACT]-> (Contract) -[PRIME]-> (Company 1) -[SUB]-> (Company 2)
The problem I'm struggling with is that the [SUB] relationship is only for certain contracts -- not all. For example:
Agency 1 -HAS-> Contract ABC -P-> Company 1 -S-> Company 2
Agency 1 -HAS-> Contract ABC -P-> Company 3 -S-> Company 4
Agency 2 -HAS-> Contract XYZ -P-> Company 1
Agency 2 -HAS-> Contract XYZ -P-> Company 4 -S-> Company 2
I want some way to search on that so I can ask cypher questions like "Find ways Agency 2 can put money on contract with Company 2." It should come back with the XYZ contract through Company 4, and NOT the XYZ contract through Company 1.
It seems like maybe storing and filtering on data within the relationship would work, but I'm struggling with how. Can I say Prima and Sub relationships have a property, "contract_id" that must match Contract['id']? If so, how?
Edit: I don't want to have to specify the contract name for the query. Based on #MarkM's reply, I'm thinking something like:
MATCH (a:Agency)-[:HAS]-(c:Contract)-[:PRIME {contract_id:c.id}]
-(p:Company)-[:SUB {contract_id:c.id}]-(s:Company)
RETURN s
I'd also like to be able to use things like shortestPath to find the shortest path between an agency and a contractor that follows a single contract ID.
I'd create the subcontractor by having two relationships, one to the contractor and one to the contract.
(:Agency)-[:ISSUES]->(con:Contract)-[:PRIMARY]->(contractor:Company)
(con:Contract)-[:SECONDARY]->(subContractor:Company)<-[:SUBCONTRACTS]-(contractor:Company)
Perhaps you can mode your use-case as a graph-gist, which is a good way of documenting and discussing modeling issues.
This seems pretty simple; I apologize if I've misunderstood the question.
If you want subcontractors you can simply query:
MATCH (a:Agency)-[:HAS]-(:Contract)-[:PRIME]-(p:Company)-[:SUB]-(s:Company) RETURN s
This will return all companies that are subcontractors. The query matches the whole pattern. So if you want XYZ contract subcontractors you simply give it the parameter:
MATCH (a:Agency)-[:HAS]-(:Contract {contractID: XYZ})-[:PRIME]-(p:Company)-[:SUB]-(s:Company) RETURN s
You'll only get company 2.
EDIT: based on your edit:
"Find ways Agency 2 can put money on contract with Company 2"
This seems to require some domain-specific knowledge which I don't have. I assume Agency 2 can only put money on subcontractors but not primes?? I might help if you reword so we know exactly what your trying to get from the graph. From my reading it looks like you want all companies that are subcontractors under Company 2's contracts. Is that right?
If that's what you want, again you just give Neo the path:
MATCH (a:Agency: {AgencyID: 2)-[:HAS]
-(c:Contract)-[:PRIME]-(:Company)-[:SUB]-(s:Company: {companyID: 2)
RETURN c, s
This will give you a list of all contracts under XYZ for which Company 2 is a subcontractor. With the current example, it will one row: [c:Contract XYZ, s:Company 2]. If Agency 2 had more contracts under which Company 2 subcontracted, you would get more rows.
You can't do this: [:PRIME {contract_id:c.id}] [:SUB {contract_id:c.id}] because Prime and Sub relationships shouldn't have contract_id properties. They don't need them — the very fact that they are connected to a contract is enough.
One thing that might make this a little more complicated is if the subcontractors also have subcontractors, but that's not evident.
Okay take 2:
So the problem isn't captured well in the original example data — sorry for missing it. A better example is:
Agency 1 -HAS-> Contract ABC -P-> Company 1 -S-> Company 2
Agency 1 -HAS-> Contract XYZ -P-> Company 1 -S-> Company 3
Now if I ask
MATCH (a:Agency)-[:HAS_CONTRACT]-(ABC:Contract {id:ABC})-[:PRIME]
-(c:Company)-[:SUBS]-(c2) RETURN c2
I'll get both Company 2 and 3 even though only 2 is on ABC, Right?
The problem here is the data model not the query. There's no way to distinguish a company's subs because they are all connected directly to the company node. You could put a property on the sub relationship with the prime ID, but a better way that really captures the information is to add another contract node under company. Whether you label this as a different type depends on your situation.
Company1 then [:HAS] a contract which the subs are connected to. The contract can then point back to the prime contract with a relationship of something like [:PARENT] or [:PRIME] or maybe from the prime to the sub with a [:SUBCONTRACT] relationship
Now everything becomes much easier. You can find all subcontracts under a particular contract, all subcontracts a particular company [:HAS], etc. To find all subcontractors under a particular contract you could query something like this:
MATCH (contract:Contract { id:"ContractABC" })-[:PRIME]-(c:Company)
-[:HAS]->(subcontract:Contract)-[:PARENT]-(contract)
WITH c, subcontract
MATCH (subcontract)-[:SUBS]-(subcontractor:Company)
RETURN c, subcontractor
This should give you a list of all companies and their subcontractors under contract ABC. In this case Company 1, Company 2 (but not company 3).
Here's a console example: http://console.neo4j.org/?id=flhv8e
I've left the original [:SUB] relationships but you might not need them.
I need to model the following relationships and would like some advice on how to properly model it.
There is a user, house, apartment, garden, furniture
So a user can either have a house or an apartment but not both.
Both house and apartment can have furniture but only the house can have garden.
So the biggest issue is user has_one house | has_one apartment, how can I model this ?
Consider using single table inheritance for this (a little wasteful because of all the null gardens, but depending on the scale of your db, that may not end up being an issue), or possibly a polymorphic relationship (user has_one dwelling).