Inheriting Parent Table with identifier (Postgres) - postgresql

Sorry if this is a relatively easy problem to solve; I read the docs on inheritance and I'm still confused on how I would do this.
Let's say I have the parent table being car_model, which has the name of the car and some of it's features as the columns (e.g. car_name, car_description, car_year, etc). Basically a list of cars.
I have the child table being car_user, which has the column user_id.
Basically, I want to link a car to the car_user, so when I call
SELECT car_name FROM car_user WHERE user_id = "name", I could retrieve the car_name. I would need a linking component that links car_user to the car.
How would I do this?
I was thinking of doing something like having car_name column in car_user, so when I create a new data row in car_user, it could link the 2 together.
What's the best way to solve this problem?


Inheritance is something completely different. You should read about foreign keys and joins.
If one user drives only one car, but many users can drive same car, you need to build one-to-many -relation. Add car_name to your user table and JOIN using that field.

Related

How to query a parent table and inherited child table together in one query

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.

Create One-to-One relationship based on PK of both tables

I'm really new to Entity Framework (currently using EF5) and vs2012 and am having difficulty trying to figure something out.
I have an .edmx that was generated from my database. It has two tables in it: Item and 3rdPartyItem. In short, the Item table is the main table for all the company items while the 3rdPartyItem table is a table that is used to hold additional attributes for items. This 3rdPartyItem table was created by an outside company and is used with their software for the company, so I can't mess with either table. What I'm trying to do is show a list of Items in a grid but I need to show a combination of all the fields for both tables. In vs2012, if I create a relationship and make it 'zero-to-one' (because for each record in the Item table, there doesn't necessarily have to be one in the 3rdPartyItem table), vs complains about not being mapped correctly. When I set the mapping, it then complains that there's multiple relationships. I did some research and found that you can't create a relationship with 2 primary keys, so I was thinking that was the problem. But how can I change the .edmx so that in code, I can access Items and 3rdPartyItem like so:
var items = dbContext.Items;
items.3rdPartyItem.SomeField <--field from 3rdPartyItem table.
not too sure if it's even possible, but it would be very, very helpful if so. Any ideas?

What you're looking for is table-per-type (TPT) mapping inheritance. You can view an MSDN walkthrough here (although you'd want your base type to be instantiable):
http://msdn.microsoft.com/en-us/data/jj618293.aspx

No-sql relations question

I'm willing to give MongoDB and CouchDB a serious try. So far I've worked a bit with Mongo, but I'm also intrigued by Couch's RESTful approach.
Having worked for years with relational DBs, I still don't get what is the best way to get some things done with non relational databases.
For example, if I have 1000 car shops and 1000 car types, I want to specify what kind of cars each shop sells. Each car has 100 features. Within a relational database i'd make a middle table to link each car shop with the car types it sells via IDs. What is the approach of No-sql? If every car shop sells 50 car types, it means replicating a huge amount of data, if I have to store within the car shop all the features of all the car types it sells!
Any help appreciated.

I can only speak to CouchDB.
The best way to stick your data in the db is to not normalize it at all beyond converting it to JSON. If that data is "cars" then stick all the data about every car in the database.
You then use map/reduce to create a normalized index of the data. So, if you want an index of every car, sorted first by shop, then by car-type you would emit each car with an index of [shop, car-type].
Map reduce seems a little scary at first, but you don't need to understand all the complicated stuff or even btrees, all you need to understand is how the key sorting works.
http://wiki.apache.org/couchdb/View_collation
With that alone you can create amazing normalized indexes over differing documents with the map reduce system in CouchDB.

In MongoDB an often used approach would be store a list of _ids of car types in each car shop. So no separate join table but still basically doing a client-side join.
Embedded documents become more relevant for cases that aren't many-to-many like this.

Coming from a HBase/BigTable point of view, typically you would completely denormalize your data, and use a "list" field, or multidimensional map column (see this link for a better description).
The word "column" is another loaded
word like "table" and "base" which
carries the emotional baggage of years
of RDBMS experience.
Instead, I find it easier to think
about this like a multidimensional map
- a map of maps if you will.
For your example for a many-to-many relationship, you can still create two tables, and use your multidimenstional map column to hold the relationship between the tables.
See the FAQ question 20 in the Hadoop/HBase FAQ:
Q:[Michael Dagaev] How would you
design an Hbase table for many-to-many
association between two entities, for
example Student and Course?
I would
define two tables: Student: student
id student data (name, address, ...)
courses (use course ids as column
qualifiers here) Course: course id
course data (name, syllabus, ...)
students (use student ids as column
qualifiers here) Does it make sense?
A[Jonathan Gray] : Your design does
make sense. As you said, you'd
probably have two column-families in
each of the Student and Course tables.
One for the data, another with a
column per student or course. For
example, a student row might look
like: Student : id/row/key = 1001
data:name = Student Name data:address
= 123 ABC St courses:2001 = (If you need more information about this
association, for example, if they are
on the waiting list) courses:2002 =
... This schema gives you fast access
to the queries, show all classes for a
student (student table, courses
family), or all students for a class
(courses table, students family).

In relational database, the concept is very clear: one table for cars with columns like "car_id, car_type, car_name, car_price", and another table for shops with columns "shop_id, car_id, shop_name, sale_count", the "car_id" links the two table together for data Ops. All the columns must well defined in creating the database.
No SQL database systems do not require you pre-define these columns and tables. You just construct your records in a certain format, say JSon, like:
"{car:[id:1, type:auto, name:ford], shop:[id:100, name:some_shop]}",
"{car:[id:2, type:auto, name:benz], shop:[id:105, name:my_shop]}",
.....
After your system is on-line providing service for your management, you may find there are some flaws in your design of db structure, you hope to add one column "employee" of "shop" for your future records. Then your new records coming is as:
"{car:[id:3, type:auto, name:RR], shop:[id:108, name:other_shop, employee:Bill]}",
No SQL systems allow you to do so, but relational database is impossible for this job.

Tough Sql Query problem involving family relationsships

i have a many to many table relationship that involves 2 logical tables.
Record table that joins to a relation table on primaryID
Second instance of record table that joins to the relation table on ReciprocalID
The purpose of this is to show family relations within the database. Each primary Record table has one or more rows in the relationtable that shows everyother family relationship this person has in the database.
I have been tasked with trying to make a contact list that involves displaying the names of each of the children that attend this school along with their parents and contact information.
I have gotten to a point where I am able to show the children under each parent, but now I have to find a way to merge these together.
Since I have no control over the design of this database(its Education Edge 7) I have made a separate database that holds my queries and views for my reports. The school I am doing this work for only has access to CR 8.5.
Right now I have my top group in CR as the lastname of the recordstable, my second group is on the fullname of the recordstable. I have a subreport that pulls in all the child records.
I have used a case when statement in my primary view(the one described above) to convert 'daughter' and 'son' to child and 'mother' or 'father' to parent.
hopefully this hasnt rambled too much. If you need anymore information just ask.
SELECT dbo.vwEA7RelationshipsTableView.PRIMARYID,
dbo.vwEA7RecordsTableView.LASTNAME AS PRIMARYLASTNAME,
dbo.vwEA7RecordsTableView.FIRSTNAME AS PRIMARYFIRSTNAME,
dbo.vwEA7RecordsTableView.NAMEFORDISPLAY AS PRIMARYNAME,
CASE dbo.vwEA7RelationshipsTableView.PRIMARYDESC
WHEN 'Father' THEN 'Parent'
WHEN 'Mother' THEN 'Parent'
WHEN 'Son' THEN 'Child'
WHEN'Daughter' THEN 'Child'
ELSE dbo.vwEA7RelationshipsTableView.PRIMARYDESC
END AS PRIMARYDESC,
dbo.vwEA7RelationshipsTableView.RELATIONID,
vwEA7RecordsTableView_1.LASTNAME AS RELATIONLASTNAME,
vwEA7RecordsTableView_1.NAMEFORDISPLAY AS RELATIONNAME,
dbo.vwEA7RelationshipsTableView.RELATIONDESC
FROM dbo.vwEA7RelationshipsTableView INNER JOIN
dbo.vwEA7RecordsTableView ON
dbo.vwEA7RelationshipsTableView.PRIMARYID = dbo.vwEA7RecordsTableView.ID INNER JOIN
dbo.vwEA7RecordsTableView AS vwEA7RecordsTableView_1 ON
dbo.vwEA7RelationshipsTableView.RELATIONID = vwEA7RecordsTableView_1.ID
TableViews are really just recreation of the primary tables from the main database.

I have solved this issue. My sql code was good, it was a matter of formatting my internal paramaters for Crystal as well as some creative grouping.

Map one-to-many tables relationship to a single entity framework object

I have the following tables in the database (just a demo, of course):
Positions
PositionId
Limits
LimitId
PositionId
I want to left join them into a single entity (always have position, not always have a limit attached to it):
Position
PositionId
LimitId
I've seen articles regarding one-to-one mapping and "Table per type inheritence", and tried to implement the same method here, but with no sucess. Is that even possible?

I think what you want is an ordinary inner join where your foreign key (PositionID in the Limits table) is allowed to be null.

Yes and no...In my scenario, the 2nd option is the applicable one, since I don't have the same primary key in both tables. so, I must create an updateable view...The problem with updateable view is that I can't modify fields which are in different tables and expect the database to handle it, unless I use "Instead of" triggers, which I really don't want to get into at all...
So, I guess there's nothing out of the box for me...damn.
(Unless you have another idea...)
Anyways, I really thank you for your help, it's much appreciated.
Nir.