I want to join two tables in order to show the details in datagrid.
Table 1: student
primary key : id
foreign key : class_id
Table 2: class
primary key : id
class can have many students. (one to many relationship)
Any suggestions would be appreciated.
I'm using OroCRM
You need to add join part to your datagrid.yml configuration. Here is an example in documentation: https://oroinc.com/orocrm/doc/2.6/dev-guide/entities/datagrids#data-source
In case if your bundles know about each other your join may be like this (from student side):
join:
left:
- { join: student.class, alias: class }
Considering that you created entities with the correct mappins. More details can be found here -
https://www.doctrine-project.org/projects/doctrine-orm/en/2.6/reference/unitofwork-associations.html
https://www.doctrine-project.org/projects/doctrine-orm/en/2.6/reference/association-mapping.html#one-to-many-bidirectional
If only bundle which holds Class entity should know about students you have to use join table. More details is here -
https://www.doctrine-project.org/projects/doctrine-orm/en/2.6/reference/association-mapping.html#one-to-many-unidirectional-with-join-table
Related
I have 2 tables. Employee and EmployeeDetails. Employee table has the basic details like Employee Id, Department and some audit fields like Created By, Created Timestamp. EmployeeDetails table has all the personal details about the employee and same audit fields (Created By, Created Timestamp) like Employee table. Now the audit fields and Version column are part of a MappedSuperclass ModelBaseFields.
I am using JOINED Inheritance in Employee which is my base class. It extends ModelBaseFields which is a MappedSuperclass. EmployeeDetails extends Employee.
Now the problem is, whenever I try to persist the data, Employee table INSERT query is formed properly however, EmployeeDetails INSERT query is missing audit fields (Created By, Created Timestamp) and version column.
I have tried using SINGLE TABLE inheritance with Secondary table. I am getting same issue in that scenario as well.
How do I add common columns in child table?
This May be a dumb question as I am a beginner in postgreSQL but what I'm trying to do is
I have a Table called Products and inside products there is 3 columns Name, Price, Expiry Date. Now I have a second table called orders with 4 columns. Product, purchasePrice, Amount, and CountryRecieved.
All I want is to reference the Product column to the product table so it has all the Information of the product table?
Is this do able?
The key concepts you need to read up on are:
"normalisation": the process of breaking down data into multiple related entities
"foreign keys": pointers from one database table to another
"joins": the query construct used to follow that pointer and get the data back together
In your case:
You have correctly determined that the information from Products should not just be copied manually into each row of the Orders table. This is one of the most basic aspects of normalisation: each piece of data is in one place, so updates cannot make it inconsistent.
You have deduced that the Orders table needs some kind of Product column; this is your foreign key. The most common way to represent this is to give the Products table an ID column that uniquely identifies each row, and then have a ProductID column in the Orders table. You could also use the product's name as the key, but this means you can never rename a product, as other entities in the database might reference it; integer keys will generally be more efficient in storage and speed, as well.
To use that foreign key relationship, you use a JOIN in your SQL queries. For example, to get the name and quantity of products ordered, you could write:
SELECT
P.Name,
O.Amount
FROM
Products as P
INNER JOIN
Orders as O
-- This "ON" clause tells the database how to look up the foreign key
On O.ProductId = P.ProductId
ORDER BY
P.Name
Here I've used an "inner join"; there are also "left outer join" and "right outer join", which can be used when only some rows on one side will meet the condition. I recommend you find a tutorial that explains them better than I can in a single paragraph.
Assuming the name column is key in Products table and product column in Orders table refers to it, you can join the two table on related column(s) and get all the information:
select
o.*, p.*
from orders o
join products p on o.product = p.name;
I am trying to join two tables by a foreign key table in linq.
The two tables are
Items and Classes, and the foreign key table is ItemClasses (ItemId, ClassId).
My context does not have a DBSet for the foreign key table, and when I try to add it I get a model creation error.
When I saw the error, I noticed that this code referred to the foreign key table
modelBuilder.Entity<Classes>()
.HasMany(e => e.Items)
.WithMany(e => e.Classes)
.Map(m => m.ToTable("ItemClasses").MapLeftKey("ClassId").MapRightKey("ItemId"));
So it looks like I should be able to refer to the items through the class, but how do I join the tables?
I'd like to do something like this
query = from ig in myCtx.Items.AsNoTracking()
//join di in myCtx.ItemClasses.AsNoTracking() on ig.Id equals di.ClassId
join c in myCtx.Classes.AsNoTracking() on di.ClassId equals c.Id
join dd in myCtx.SalesAssociates.AsNoTracking() on dd.Id equals ig.SalesAssociateId
How do I do joins when the fk table is not in my context, but is referred to in one of the tables?
First, you have a configuration error. With HasMany / WithMany you are actually configuring the automatic "link" table, so
m.ToTable("Classes")
should be
m.ToTable("ItemClasses")
or how exactly you want that table to be named in the database.
Second, when working with EF, it's always preferred to use navigation properties rather than joins. In case of many-to-many relationship with auto link table, using navigation properties is mandatory. EF will produce the necessary joins for you.
So instead of join your would use something like this:
query = from ig in myCtx.Items.AsNoTracking()
from c in ig.Classes
...
I'm having a hard time finding the exact answer to this question, so my apologies if this is redundant.
So I have 3 tables defined such that:
Person :PersonId, FirstName, LastName
Company: CompanyId, CompanyName
Order: OrderId, PersonId, CompanyId
On the Order table, there is a foreign key defined on the PersonId and CompanyId columns, thus, my Order entity class generated by EF has a navigation properties of type Person (not PersonId) and Company.
So, to insert into the Order table, I first need to query the person and company tables to get the person and company entities. Then I can construct the Order object using the Person and Company entities and save it to the db.
In my scenario, I am being passed a PersonId and CompanyId.
In classic SQL I would just do INSERT INTO Order Set (CompanyId, PersonId) - 1 database call. But with EF, I have to do 3 db calls. This seems like overkill.
Is there any way around this?
PS - I'm using EF 6. I know I could generate an expression and make it single call..but that would still yield two subselects.
You can just include foreign key properties in addition to the navigation properties and then set them using the ids you have. If you do this will not have to go to the database to get related entities for just a sake of setting the relationship.
Hopefully my description is a little better than the title, but basically I'm having an issue with one part of a new application schema and i'm stuck on what is the most manageable and elegant solution in table structure.
Bare bones table structure with only relevant fields showing would be as follows:
airline (id, name, ...)
hotel (id, name, ...)
supplier (id, name, ...)
event (id, name,...)
eventComponent (id,name) {e.g Food Catering, Room Hire, Audio/Visual...}
eventFlight (id, eventid, airlineid, ...)
eventHotel (id, eventid, hotelid, ...)
eventSupplier (id, eventid, supplierid, hotelid, eventcomponentid, ...)
So airline, hotel, supplier are all reference tables, and an Event is create with 1 to many relationships between these reference tables. E.g an Event may have 2 flight entries, 3 Other components entries, and 2 hotel entries. But the issue is that in the EventSupplier table the supplier can be either a Supplier or an existing Hotel. So after the user has built their new event on the front-end i need to store this in a fashion that doesn't make it a nightmare to then return this data later.
I've been doing a lot of reading on Polymorphic relations and exclusive arcs and I think my scenario is definitely more along the lines or an Exclusive Arc relationship.
I was thinking:
CREATE TABLE eventSupplier (
id SERIAL PRIMARY KEY,
eventid INT NOT NULL,
hotelid INT,
supplierid INT,
CONSTRAINT UNIQUE (eventid, hotelid, supplierid), -- UNIQUE permits NULLs
CONSTRAINT CHECK (hotelid IS NOT NULL OR supplierid IS NOT NULL),
FOREIGN KEY (hotelid) REFERENCES hotel(id),
FOREIGN KEY (supplierid) REFERENCES supplier(id)
);
And then for the retrieval of this data just use an outer join to both tables to work out which one is linked.
select e.id as eventid, coalesce(h.name,s.name) as supplier
from eventSupplier es
left outer join
supplier s on s.id = es.supplierid
left outer join
hotel h on h.id = es.hotelid
where h.id is not null OR s.id is not null
My other options were to have a single foreign key in the eventSupplier table with another field for the "type" which seems to be a harder solution to retrieve data from, though it does seem quite flexible if I want to extend this down the track without making schema changes. Or alternately to store the hotelid in the Supplier table direct and just declare some suppliers as being a "hotel" though there were then be redundant data which I don't want.
Any thoughts on this would be much appreciated!
Cheers
Phil
How about handling events one-by-one and using an EventGroup to group them together?
EDIT:
I have simply renamed entities to fit the latest comments. This as close as I can get to this -- admittedly I do not understand the problem properly.
A good way to test your solution is to think about what would happen if an airline became a supplier. Does your solution handle that or start to get complicated.
Why do you explicitly need to find hotel data down the supplier route if you don't need that level of data other types of supplier? I would suggest that a supplier is a supplier, whether its a hotel or not for these purposes.
If you want to flag a supplier as a hotel, then simply put hotelid on the supplier table or else wait and hook in the supplier later via whatever mechanism you use to get detail on other suppliers.