Is it possible to have custom defined values for #rid in OrientDB?
Say in class Vehicle, i want my rid to be vehicle number
Is there any way to have user defined Ids?
Is not possible. #rid is generated by the database and identifies the position of the record (clusterId + clusterPosition)
http://orientdb.com/docs/2.0/orientdb.wiki/Tutorial-Record-ID.html
Related
Sorry if this is a relatively easy problem to solve; I read the docs on inheritance and I'm still confused on how I would do this.
Let's say I have the parent table being car_model, which has the name of the car and some of it's features as the columns (e.g. car_name, car_description, car_year, etc). Basically a list of cars.
I have the child table being car_user, which has the column user_id.
Basically, I want to link a car to the car_user, so when I call
SELECT car_name FROM car_user WHERE user_id = "name", I could retrieve the car_name. I would need a linking component that links car_user to the car.
How would I do this?
I was thinking of doing something like having car_name column in car_user, so when I create a new data row in car_user, it could link the 2 together.
What's the best way to solve this problem?
Inheritance is something completely different. You should read about foreign keys and joins.
If one user drives only one car, but many users can drive same car, you need to build one-to-many -relation. Add car_name to your user table and JOIN using that field.
I know that it is possible using #SqlResultSetMapping but I want to select not whole entity from the database but some fields and then map i to my entity using one of the constructor which accept that fields. Is that possible to map result with #EntityResult for only a few #FieldResult? I was trying to do that and all the time I get error which said that there is not specify mapping for some fields which exist in that entity.
The disadvantage of #SqlResultSetMapping is that you have to select all the columns.
The alternate way of doing this manually iterate over the DB result and populate your objects.
Well, if you are using JPA 1.0 your only option (not considering the manual mapping, of course), is to use #SqlResultSetMapping and map the whole table columns. With JPA 2.1 you can add a javax.persistence.ConstructorResult (see docs here) to map only the needed columns.
Having an entity that contains a column named "workDay" how can I make query to get all entries in a map where key is "workDay" and value a list of entities.
Any hing is welcome.
Thanks.
You want a query method to return Map<Date, List<?>>. Map is not a supported return type for query methods. Therefore, you cannot use the default implementation to achieve what you are looking for.
You can create a custom repository implementation that queries the database and returns the desired Map<Date, List<?>>.
When we have two entities in EFv4 EDM diagram and only one table for both in the database (for instance, having table Documents and entities Invoice and Qoute), table Documents having documentTypeId column as a discriminator and set this column as a discriminator in the EDM (in Table mappings), how do we read the value of this property in our code?
We cannot assign values to it because EF does it for us under the hood (based on what we entered in Table mappings for condition) but somehow I don't get it why we are also not allowed to read it.
Imo this property is already mapped so you can't map it again. It is used to determine type of materialized entity. Why do you need such column. Usually it is enough to use is operator like:
var document = context.Documents.GetById(id);
if (document is Invoice)
{
...
}
If you only need to select subtypes you can use OfType extension method like:
var invoices = context.Documents.OfType<Invoice>().ToList();
You also don't need to set this value when adding new entity because you are adding subtype - Invoice or Quote.
Edit:
As I understand from your comment you don't need this information in query. In such case you don't need to map it. Simply use partial class of your entity and add custom property which will return your string. Sound like stupid solution but actually it would be the easiest one.
Discriminator column should be part of mapping metadata so in case of T4 template generating your entities, it could be possible to update the template so it generate such property for you.
You may want to use a single-table inheritance hierarchy, as described here.
That way, you could have an abstract Document class that includes a DocumentTypeId column. Invoices and Quotes would extend this class, but specify certain DocumentTypeId filters. However, because the original class has a DocumentTypeId column, they would each have that column as well.
Another advantage to this approach is that you could create utility methods that can act on any Document, and you could pass any Invoice or Quote to these methods.
I am trying to execute a namedquery
#NamedQuery(name="getEmployeeDetails",query="select e.username,e.email,e.image,e.firstname,e.lastname from Employee e where e.empid=?1")
Now when I execute this query in a EJB 3.0 Session Bean what is the object I should return.I tried returning Listits returning a Vector which creates a classcast exception.The employee table contains fields like password and other confidential details which I don't want to fetch.So I am not using select e from Employee e.
I am learning JPA can anyone help.
Below is the sample query which fetches only the required fields, but have to make such constructor for it.
Query : SELECT NEW package_name.Employee(e.username,e.email,e.image,e.firstname,e.lastname) FROM Employee e where e.empid=?1;
It will return Employee entity with selected fields & remaining will have default values.
Inspect the returned type by calling .getClass() on a returned object. I'd guess it's an array.
But this is not really a good way to use JPA. Select the whole entity and then just don't use what you don't need. It's not such a performance hit.