Im working on an assignment where i have to create an EERD, and one of the entities (Bed) has an identifier key of Bed ID which is a composite attribute of bed# and Room #.
How should i go about setting this up as a single identifier?
Related
Lastest Realm Swift 1.0.1
I do follow this
composite primary key realm/swift
It's shows error following
How to i can write with Swift?
You will need to drop the lazy specifier from the variable declaration as how the error messages states such properties are not supported. You don't want to ignore the property as you want to use it as a primary key.
Beside that I would recommend to separate your integer components within your compound key. (e.g. "\(id)|\(tourId)") Otherwise you can end up having different objects with the same conflicting primary key. e.g. You could have objects with compoundKey="123" for the combination id=1 tourId=23, but also for id=12 tourId=3.
I have legacy tables with Primary keys. These tables also have surrogate keys that have been used to relate one table to another. I would like to map the Membership.User table (uses a Guid PK) but has a property UserName which holds the surrogate key which relates it to the DepoMembers table. DepoMembers has a numeric PK - but has a surrogate key UserName. UserNames are guaranteed to be unique.
In Linq2SQL - to relate these tables in the designer - we add an association where User.UserName is linked to DepoMembers.UserName - and set the multiplicity of the Association to 1:1. then Modify the Navigation Names to singular.
If we take DepoMembers as the Principal End of the relationship - it should follow that If Membership.User does not exist (As in the case - where a user does not manage the application site but exist in DepoMembers) the Navigation Property User will be Null.
How can this be done in Code First ...
The only alternative I've come up with so far is to create a property DepoMembers.User which uses the UserName Property to retrieve the User using the datacontext.
Ren
I have an linq to entity mapping issue. I have three tables.
Table 1 - ItemsB(ID(key), Part_Number(will be null until built), other item b information)
Table 2 - ItemsA(ID(key), Part_Number(will be null until built), other item a information)
Table 3 - WebItems(Item_id, web item information) *Consists of items from both ItemsB and ItemsA after they are built and pushed over to this table.
ItemsA/ItemsB will have a 1 to 0.1 relationship with WebItems. Part_Number maps to Item_id.
I am using EF4.0.
Problem is after i set up the association/mappings as stated above i get an error message stating: "Problem in mapping fragment at lines so and so: Column [Part_Number] are being mapped in both fragments to different conceptual side properties."
Usually i know what to do in this case. Get rid of the property [Part_Number]. Problem is i need to access [Part_Number] in both ItemsB and ItemsA quite frequently without going to webitems. Not to mention webitems will not always have the [Part_Number] populated at certain points depending upon whether the items have be pushed to webitems.
Does anyone know how to get around this?
Thanks in advance.
As I understand it ItemA and ItemB to WebItem in one-to-one relation. One-to-one relation in EF always demands that relation is build on primary keys and one side is mandatory (principal) because dependent entity will have primary key and foreign key in one column. Once you assign primary key in dependent entity you must have principal entity with the same primary key otherwise you will violate referential integrity defined by foreign key.
The problem is that your Part_Number is primary key and foreign key in the same time. To allow such mapping in EFv4 you must use Foreign Key association instead of Independent association. Here is brief description how to create foreign key association in the designer. Once you define referential constrain get back to mapping window of association and delete the mapping.
I'm sure I'm missing something very simple, but let's say I have two entities, Employee and EmployeeType.
Employee type would contain values like 'Full time', 'Contractor', 'Intern', etc.
An Employee entity would contain one, and only one EmployeeType value.
So I am designing a new .edmx model using the Model-First approach and generating my actual sql server data schema from the model.
I want to add an integer type foreign key id into my Employee entity, EmployeeTypeId, which will map to the primary key of the EmployeeType entity.
So I've gone ahead and done that in my Employee entity. Where I'm stuck is how, though the Entity Framework designer, to enforce the 1:1 referential constraint on that EmployeeTypeId property? Or does the EF handle that automatically behind the scenes?
thanks in advance,
John
Think I figured out the answer to my own question. In the EF .edmx surface designer, I needed to right click on the scalar property I wanted to set as a foreign key id to the other entity and choose 'Entity Key'.
Once that was done, I could go into the referential constraints dialog box and point my new foreign key property to the other entity.
If you don't explicitly set your foreign key property as 'Entity Key', EF will think you want to point your primary key id to the other table.
cheers
You first create a new association (if you haven't done this already) between the two entities. Just right-click on the edmx designer and choose Add -> Association.
When you click on the association you have just created in the model designer, in the properties window, you can set the End1 Multiplicity and End2 Multiplicity properties to 1. This will ensure that you can set only one relation entity while using the entity framework. This does not get enforced in SQL server by the way, because SQL server does not implicitly support 1:1 relationships.
I'm getting more and more frustrated with EF...
I have a table called ExtendedField with:
Record
DocRef
DocType
Name
Record is the primary key
DocRef and DocType are foreign keys used to identify which Ticket they belong to
Name is the key used by the "definition" table to define what the field actually is
So basically I need 2 associations:
One between Ticket and ExtendedField
on ExtendedField.DocRef=ticket.record
and
ExtendedField.docType=HeaderDocType
One between Definition on
ExtendedField.Name=Definition.FieldName
Then I still need Record to be the primary key so I can directly access the fields.
As near as I can tell this is impossible to do in Entity Framework. For every association all the keys need to be mapped together, whereas I need two keys for one association, 1 key for another one and the actual primary key wouldn't be used in any associations.
It doesn't appear that you can define an association between fields that aren't entity keys either.
So is there any way to do this? Am I missing something?
It's a v1, bro. I myself have had some major pain with mapping of key constraints in EF. I hear that better things are coming in v2.