I'm trying to model the following relationships between entities, mainly consisting of a partial, disjoint generalization.
original EERD
'mapped' to relational
Since I didn't need the subclasses to have any particular attributes I decided to use the "single table inheritance" approach, added the "type" field and moved the relationships towards the parent.
After that I had two choices to make:
1- type for the "business type" attribute
2- way to constraint participation to at most one of the 4 relationships based on the type attribute
For the sake of portability and extensibility I decided to implement no.1 as a lookup table (rather than enum or a hardcoded check).
About no.2 I figured the best way to enforce participation and exclusivity constraints on the four relationships would be a trigger.
The problem is that now I'm not really sure how to write a trigger function; for instance it would have to reference values inserted into business type, so I'd have to make sure those can't be changed or deleted in the future.
I feel like I'm doing something wrong so I wanted to ask for feedback before going further; is this a suitable approach in your opinion?
I found an interesting article describing a possible solution: it feels a bit like an 'hack' but it should be working
(it's intended for SQL Server, but it can be easily applied in postgres too).
EDIT:
It consists in adding a type field to the parent table, and then have every child table reference said field along with the parent's id by using a foreign key constraint (a UNIQUE constraint on this pair of fields has to be added beforehand, since FKs must be unique).
Now in order to force the type field to match the table it belongs to, one adds a check constraint/always generated value ensuring that the type column always has the same value
(eg: CHECK(Business_type_id = 1) in the Husbandry table, where 1 represents 'husbandry' in the type lookup table).
The only issue is that it requires a whole column in every subclass, each containing the same generated value repeated over and over (waste of space?), and it may fall apart as soon as the IDs in the lookup table are modified
The objective:
Having a many-to-many relation be displayed as a dynamic list of select inputs(single choice dropdown list)
User arrives on page with a single select field (multiple = false) populated with persisted entities and add/remove buttons. By clicking the add button, a new select field with the same options appears below the first, which adds a new entry in the M2M relation. By clicking remove the field disappears and the entry should be removed.
The model:
Two entities: User & Manager. A User has exactly one "special" Manager and unlimited normal Managers.
Managers manage unlimited users.To model this I have created two relationships for which the user is the "owner" (not sure how to translate this)
ManyToOne specialManager
ManyToMany normalManagers
I haven't created a many to many relationship with attribute "special" because the requirement is exactly one special manager and I wasn't sure if Symfony/Doctrine would cause problems down the line.
What I have:
I can display a multiple select field with the existing entities using Entity field type, as per the documentation. Functionally this is what I need, visually it is not.
I can also use the Collection field type to display a single text field, and add or remove more with JS, as per the documentation. Visually this is what I need, but The text fields (entity attribute) need to be replaced by choice field.
The question:
Before I continue digging, is there a simple way to achieve this list of select tags?
For anyone else who may eventually need a dynamic list of select fields:
I initially solved this issue by detaching the field(s) in event listeners, and handling the display/submission manually in the controller.
However I wasn't satisfied with this clunky solution and when I encountered the same need I used a second solution: creating an intermediary entity xxxChoice (in this case ManagerChoice) which is Mto1 inversed related to User and Mto1 related to Manager. Then by creating a ManagerChoiceType form with "Manager" entity field type I was able to easily display my collection of dropdown select lists.
I have an entity model built using the designer. In one of my tables (application), I have several foreign keys that reference the same status (status) table. As a result, when my associations were built, I have several entity objects built with an auto indexing name:
application_statuses2
application_statuses3
etc.
I'm building a "version history" type screen and want to be able to properly list the "friendly name" for each column modified. For example, I want to display "Destination Status" will be displayed instead of "application_statuses2". If I can determine the endpoint column name on the association in question, I can setup the proper display value.
I can find the entity object in the designer, I can even track where it references the foreign key in question that built the association, but I can seem to find the property that outlines the enpoints or column names. How do I determine the column name, or endpoint, on my association, or entity?
I wish it were more ready to hand, have been looking for it as well. Bit of a pain when you have multiple FKs to the same table.
Click on the navigation property you want to check
Under properties, look at the name of the association
At the top of properties, use the object navigator dropdown to switch to the association
Click into the 'Referential Constraint' property
Use the ellipses button on the right to bring up the column names
Dont know if there is a better way of doing this, but I certainly hope so!
I want to use a Money value object in my application. I have found several examples of a Money datatype. But I can't figure out how to use them with EF4. I would like to store each amount as a Decimal/CurrencyCode pair (where currencycode is a string - "USD", "SEK", etc) in the database. I tried creating a complexType but I couldn't get that to work. Is this possible?
It should be definitely possible. Your complex type is just pair of decimal and string property. It is exactly what complex type are used for. Depending on your approach you must do:
Database first:
You will define your database first. Your table will contain money and varchar columns representing your new type. When you update your EDMX model from database it will include it as scalar properties to your entity. You must remove those properties. Then go to model browser and create new complex type. Return back to entity and add complex property of your new complex type. And at the end you must go to entity mapping and map your complex type to those database columns.
Here is basic tutorial from MSDN but from unknown reason they didn't include such elementary details like screenshots. Here is some video from channel9.
Model first:
This is similar to database first but you don't have to deal with database creation and mapping. It will be generated for you.
Code first (EF 4.1):
You must create separate class for your complex type and use it as property in your entity. You should not need to map it by default - mapping should be infered. If it doesn't work you can map complext type either by using ComplextTypeAttribute annotation or by defining mapping in DbModelBuilder.
I can further extend approach you need to use if you provide more details.
Error 3007: Problem in Mapping Fragments starting at lines 186, 205: Non-Primary-Key column(s) [WheelID] are being mapped in both fragments to different conceptual side properties - data inconsistency is possible because the corresponding conceptual side properties can be independently modified.
I found several places on the web describing this error, but I simply don't understand them. (confused smiley goes here)
One
Two
Three
Four
There is something pretty fundamental here, I must be missing. Can you explain it, so that I understand it? Maybe using my real life example below?
Foreign key 1:N Wheels.Id -> Slices.WheelId
I add them to entity framework, and WheelId is not visible in the Slices-entity.
Doing some workaround (deleting the relationship from the db before adding tables to EF - then re-creating it and updating EF) I managed to get the WheelId to stay in Slices, but then I get the error mentioned at the top.
Since Slices.WheelId is an FK, you cannot expose it in your client model, period. There are ways to get the value, though.
var wheelId = someSlice.Wheels.ID;
Update In EF 4 you can do this by using FK Associations instead of independent associations.
Try to remove foreign property column from Entity set using entity model design it will solve your problem
For example
We have two tables one is customer and other one is order, using entity model design we added association between customers and orders when we do this Ado.net entity framework i will add navigation properties to both below tables.
Like
Customer.Orders - Here order is list
Order.Customer
One - Many relation.
So we need to remove property from with name CustomerId[Foreign key column] from Order entity set.
For reference:
http://social.msdn.microsoft.com/forums/en-US/adodotnetentityframework/thread/2823634f-9dd1-4547-93b5-17bb8a882ac2/
I was able to overcome this problem by the following steps:
right click the designer window
Select 'update model from database'
Select Add AND make sure that the 'Include foreign key columns in the model' checkbox is selected.
click on Finish...
I had set foreign keys up in the database but framework still wasn't pulling them in correctly. So I tried to add the association myself.
However, when I did this I would get a mapping error. It took me A WHILE but I figured out. What I did was set up the association using the entity toolbox association tool and then you have to double click on the association (1 to many) line and set the primary and foreign key there. Hopefully, this to help others who might have the same problem. I couldn't find the answer anywhere.
I had this problem for quite a different reason, and the message was slightly different; it didn't say "data inconsistency is possible because the corresponding conceptual side properties can be independently modified."
I have a table involved in my model with a binary column where I store image data. I only want this data returned when I need it (performance is a feature), so I split the table using a method similar to this. Later on, I added a property to that table, then updated the model from the database. The wizard added the property to both entity types that refer to the table with the added property. I had to delete it from one of them to solve the error.
I've had this happen because Entity Framework Update wizard mismapped some keys (or did not update?). As a result, some columns were mistakenly labeled as keys, while actual key columns were treated as plain columns.
The solution was to manually open EDMX file, find the entities, and update the keys.
Couldn't get any of the answer to work with EF6. The problem seems to be the framework doesn't import the foreign keys correctly as Associations. My solution was removing foreign keys from the tables, and then manually adding the associations using Entity Framework model, using the following steps: Entity Framework - Add Navigation Property Manually
For LinQ to Entities queries in EF1, my workaround for not having access to the foreign key as a property is with the following code, which does not produce a join query to the associated table:
dbContext.Table1s.FirstOrDefault(c => (int?)c.Table2.Id == null)
i.e, the generated SQL is:
...WHERE ([Extent1].[Table2Id] IS NULL)...
Solution is to allow deleting Rule = Cascade on Sql association.
Same thing as to be done on .edmx model, adding element to
association:
<Association Name="FK_Wheels_Slices">
<End Role="Wheels" Type= "your tipe here" Multiplicity="1">
<OnDelete Action="Cascade" />
</End>
</Association>
I had a table already mapped in EF. I added two more tables which had foreign keys in the previously added table. I then got the 3007 error.
To fix the error I deleted all three tables from the EDMX file, and then re-added them all at once together (via "Update Model from Database..."), instead of in stages.
I checked my Error List window and noticed I had errors in the model. Fixed them and all is well
in my case I solved this error by tick (include foreign key columns in the model)
- update Model from database
- tick (include foreign key columns in the model)
- finish