I have an obect called "Task" and each task has a type. In my database design without ORM, i would have a table called TaskTypes and Task table would have foreign key to the TaskTypes table where we define Tasks..
Is there a way to handle this behaviour natively in jugglingdb? Or do i have to create another model called TaskTypes and make Task "belongTo" a TaskType class?
The "native" way to handle this would be to define each model.
You can take a slight shortcut with Task.belongsTo('tasktype'); which will add the column tasktypeId for you.
Related
I have a GraphCool model called Student which has a field called studentNumber. How can I prevent two (or more) different Student nodes with the same studentNumber? In SQL databases I was able to create a unique index to accomplish this.
The easiest way to do so is by enabling the "Unique" constraint for a certain field (studentNumber in your case for the Student model). You can enable constraints in the structure view when editing a model.
Note: Under the hood, this creates a unique index in the database just like you suggested.
On a Lead it is possible to insert Associations, when I qualify a Lead, a Opportunity is made, which shows Associations lines.
I want to insert the associations from the Lead into the opportunity in AX2012.
I have found out the associations in the Lead is using the smmLeadRelTable, the Opportunity is using the smmOpportunityRelTable.
How can i insert the association? I don't see the relation between these tables and I can't figure how to start to initialize these values?
The smmLeadRelTable as well as the smmOpportunityRelTable table references leads and opportunities using the RefTableId/RefRecId pattern. This pattern allows for generic references in cases where it is not clear at design time what tables will be referenced or where a number of different tables should be referenced. To create a reference, you would initialize the RefTableId field with the id of the table that is to be referenced. You would then initialize the RefRecId with the RecId of the record from that table that is to be referenced.
To fulfill your requirement you want to transfer the entries in smmLeadRelTable to smmOpportunityRelTable, replacing the LeadId with the OpportunityId. The entries in smmOpportunityRelTable are created in method createLinkRelation in class smmCreateEntity. There you could add an EventHandler or edit the method directly to add your logic that will create an entry in smmOpportunityRelTable for each opportunity relation in smmLeadRelTable.
I’m in a dilemma choosing the best strategy to model my database.
Let’s say I have a two tables: Variable(ID) and Object(ID).
Now, an entry in Variable may reference another entry in Variable or in Object.
To model this, one approach is creating 2 mapping tables:
Variable_Variable(variable_id, variable_id), Variable_Object(variable_id, object_id)
The other approach is to have in the Variable table two reference columns:
Variable(ID, parent_variable_id, parent_object_id).
If this variable references another variable, then the parent_object_id is null and vice-versa.
I feel first approach is neater, but second approach is faster when querying the database.
Is there any standard to apply in this cases? Which is the usual approach for these cases?
Thanks,
Danny.
Given that all relations are 1:1 I would go with your second approach of having parent_variable_id and parent_object_id columns in your Variable table.
You could then have a CHECK constraint to ensure that only one or the other column contains a value (or neither, if your variables don't have to reference a parent).
Another alternative that you didn't mention is using a single mapping table MappingTable (variable_id, parent_variable_id, parent_object_id). The downside with this is that, if variables must have a parent, you will then have to enforce a 1:1 relationship between the Variables table and Mappings table.
I would only consider using a mapping table if modelling an n:n relationship, or if there is additional information about the relationship between a variable and it's parent that needs to be recorded.
Currently I have a table "ComponentAnalysis" and a table "HistoryOfUse" that I am trying to map in Fluent NHibernate.
A component analysis should only have 1 history of use and a history of use should belong to 1 component analysis. This would suggest to me that the tables should be set up for a 1 to 1 mapping. But the designer of the DB didn't set it up that way.
Instead "HistoryOfUse" has a column "ComponentAnalysisID" to specify what component analysis it belongs to. To conform to the database I should have HistoryOfUse References ComponentAnalysis and ComponentAnalysis should HasMany HistoryOfUse.
But if I do this then I need to have a list of type HistoryOfUse which seems fairly annoying. Is there a way to set this up, without changing the database, to allow ComponentAnalysis to have a single HistoryOfUse object even though, according to the DB structure, it should have a list of them?
You can use HasOne method to map your classes. Here is the detailed article about this.
Your class ComponentAnalysis will "HasOne(x => x.HistoryOfUse)". Column HistoryOfUse.ComponentAnalysisID should be a unique key and a foreign key referenced to the ComponentAnalysis.ID column.
I've got a parent and child object. Depending on a value in the parent object changes the table for the child object. So for example if the parent object had a reference "01" then it will look in the following table "Child01" whereas if the reference was "02" then it would look in the table "Child02". All the child tables are the same as in number of columns/names/etc.
My question is that how can I tell Fluent Nhibernate or nhibernate which table to look at as each parent object is unique and can reference a number of different child tables?
I've looked at the IClassConvention in Fluent but this seems to only be called when the session is created rather than each time an object is created.
I found only two methods to do this.
Close and recreate the nhibernate session every time another dynamic table needs to be looked at. On creating the session use IClassConvention to dynamically calculate the name based on user data. I found this very intensive as its a large database and a costly operation to create the session every time.
Use POCO object for these tables with custom data access.
As statichippo stated I could use a basechild object and have multiple child object. Due to the database size and the number of dynamic table this wasn't really a valid option.
Neither of my two solutions I was particularly happy with but the POCO's seemed the best way for my problem.
NHibernate is intended to be an object relational mappers. It sounds like you're doing more of a scripting style and hoping to map your data instead of working in an OOP manner.
It sounds like you have the makings of an class hierarchy though. What it sounds like you're trying to create in your code (and then map accordingly) is a hierarchy of different kinds of children:
BaseChild
--> SmartChild
--> DumbChild
Each child is either smart or dumb, but since they all have a FirstName, LastName, Age, etc, they all are instances of the BaseChild class which defines these. The only differences might be that the SmartChild has an IQ and the DumbChild has a FavoriteFootballTeam (this is just an example, no offense to anyone of course ;).
NHibernate will let you map this sort of relationship in many ways. There could be 1 table that encompasses all classes or (what it sounds like you want in your case), one table per class.
Did I understand the issue/what you're looking for?