I have a question in Entity Framework.
I have two tables: Customers and Addresses
The Customers table contains information about customers and Addresses contain information about the customer address. Both tables are linked together by CustomerID.
How can I get all Customers objects (from Customers) who are living in the USA (from Addresses) ?
Can anyone help?
You can use .Where like this:
List<Customer> usaCustomers = dbcontext.Customers.Where(c => c.Address.Country == "USA");
This assumes that:
Each customer has only one address
Address entity has Country property
Related
Is it possible to reference additional columns apart from the 'Code' and 'Name' columns when using a domain attribute in an entity?
E.g. A person entity has a code of '1' and a name of 'Smith' and a Gender of 'Male'
In a customer entity there is a domain value referencing the person entity which displays the following 1 {Smith}. The users would like an additional read only attribute which would copy the Gender value of 'Male' into the customer entity based on the domain value. Can this be done using out of the box MDS UI?
I know this is duplicate data and breaks normal form but for usability this would be useful. It would be the equivalent of referencing additional columns in an MS Access drop down list.
Many thanks in advance for any help
This is not possible with the standard UI. One option would be to develop a custom UI where you can handle these kind of requests.
If you want to stick with the standard product I can see a workaround but this is a bit of a "dirty" one.
You can misuse (abuse) the Name attribute of the Person entity by adding a business rule to the Person entity that generates the content of the Name attribute as a concatenation of multiple attributes. You of course need an additional attribute that serves as a place holder for the original Name. The concatenated field will then show in your customer entity.
One question that does come to mind is why a user would like/need to see the gender of a person in a customer list? As you have a separate Person entity I expect you to have multiple persons per customers. What would the gender of one person - even if it is the main contact - matter?
I have a table named product having product id, product bill id and.. the bill id is passed to my controller as a parameter.
I can use the entities from framework and find all rows with product id using
db.tbl_product.Find(product id).
But now i need to find all transactions using bill id. How do I do that??
Assuming tbl_product is a DbSet<Product> or something similar, you should be able to use LINQ to query the DbSet. To find a single item with a specific BillId property value, you would do something like this:
var product = db.tbl_product.FirstOrDefault(p => p.BillId == billId);
If there were multiple products with the same BillId, you could do the following:
var products = db.tbl_product.Where(p => p.BillId == billId);
It largely depends on the schema of the table and how you're using Entity Framework. I would highly recommend reading a book or tutorial on Entity Framework. There are lots of them out there, for example: Entity Framework Tutorial.
I load list of invoices, and I also loaded list of customers, using the same context. If I want to display invoices in a grid, where one column will contain customer's name, I need to somehow fix-up the relationship between the invoices and the customers.
How can I do this?
The problem was that customers list was retrieved with MergeOption.NoTracking, so it was detached from context, and it could not look for relationship.
I'm having a little trouble grasping CoreData relationships, i'm note sure which relationship type I should be using between my 2 entities or if my logic is correct.
1) "Person" Entity - attributes such as name, tel, address, country, etc...
2) "CountryList" - attributes such as countryName, countryLat, countryLong, etc..
The CountryList entity is pre populated on first run of the app to include all the countries in the world and their respected data.
Where i'm stuck is do I need a relationship between these two entities?
I will be allowing the user to select a country from the CountryList entity data and wish to store there selection in the country attribute for Person entity.
Do I just take the countryName from CountryList as a string and store it in country from Person? or can I make a relationship between them?
I know a user can only belong to 1 country but a country can have lots of users so is this a one to many relationship? Or is it many to many because lots of users can belong to a country but a country can have loads of users? Confused!
Could someone please enlighten me on this and point me in the right direction in what i should be doing in xcode.
Many Thanks in Advance
Matt
EDIT: Is this correct?
I have made the changes to Entity names etc and think I now have the relationship set correctly.
EDIT 2: Removed country attribute and renamed relationships
Firstly, your "CountryList" entity should be called "Country", since it represents only one country. The fact that you have many of those countries has nothing to do with its name.
After that, it seems just natural to use a relationship, one "Person" has one "Country", but one country can have many persons. Therefore, one-to-many relationship. Using a relationship will simplify many operations you might want to perform (i.e. access all the country information of one person, or get a list of all persons being in one particular country).
Oh, and this might help you understand relationships a bit better: There are no "many-to-many" relationships in CoreData per se. You always define a relation from a source to a target. So if you define a relation from Country to Person, this will be a one-to-many relationship. One country, many persons. You can then define a relationship from Person to Country, which would be a one-to-one relationship. One person, one country. If you defined this as an one-to-many relationship, you would end up with a de facto many-to-many relationship (because on person can have many countries and one country can have many persons). It's not as complex as it appears.
Now, after you've defined your two relationships, you can set them as each others "Inverse Relationship". Do it for one of the relationships, the other one will be set automatically. After you did that, CoreData will for example update a Person's country when you add the person to the country's list.
See https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CoreData/Articles/cdRelationships.html for further information.
CountryList should just be Country
Then you set a 'many to one' relationship between Person.county and Country
You are using Core Data so you must define relationship between Person and Country if you want to fetch person's country from database.
And in this relationship you may take one to one relationship. As One person will belong to one country only. Of Course a country will have many person but unless you want to show all people related to particular country you do not need one to many relationship..
In case you want to implement one to many relationship this tutorial link maybe helpful to you for understanding one to many relationship..
http://www.theappcodeblog.com/2011/09/29/iphone-app-development-tutorial-core-data-part-2-one-to-many-relationship/
Amongst order tables i have a Customers table and Addresses table. A customer can have many addresses so I have setup a one-to-many relationship in a yaml file. The thing is the id for the Customers table is auto generated so I would not know the Customers_id until after the insert however, the Customers_id is a foreign key in the Addresses table.
The information for both tables is captured on the same form although each set of data is in a subform. How do I get Doctrine to insert the data into the Customers table then fetch the Customers_id just entered and use it as the foreign key for the Addresses table.
Hope I have been able to get the essence of the question across.
BTW I am using Zend Framework and Doctrine 1.2.3
Once you do $customer->save(), you may use $customer->id (if "id" is the Customers_id column name of your customer table) to get the Customers_id to put in Addresses table.
Once you do $customer->save(); the following statement $customer->identifier(); should give you the id.
Assuming you are using Doctrine 1.x you could do the following:
$cusomer->Address[] = $address; // Assign multiple addresses in this manner
$customer->save();
This will first save the customer details to the db and then store the address data. Since doctrine understands the relationship between customer and address, the ORM will insert the customer id in the address table. Further this will be run within a transaction by Doctrine which ensures that if one of the operations fail the entire transaction will be rolled back.