The usage in our code doesn’t need to be changed at all. So currently we have the hybrid of both types of relationships within out two models. So the model class finally looks as follows:Īs you can see, we have just created many-to-one relationship by using ManyToOneAttribute. To realize the above class diagram and make each children (each Duty in our case) knowing about its parent (having a reference to responsible Employee), the only thing we need to do is to add the following property to Duty model class: What changed is that now each Duty has a property of type Employee. One-to-many with inversion (one-to-many + many-to-one)Īs previously, let’s first see how the class diagram changes after adding inversion: One-to-many with inversion – class diagram Moreover, each children has its foreign key ( EmployeeId) automatically retrieved from the DB – there is no overhead here, this is simply foreign key field stored in the same SQLite database table ( Duties). What’s interesting for us it how employeeStored looks in the end: One-to-many with no inversionĪs you can see, GetWithChildren method returned object of type Employee with its Duties collection properly retrieved (containing two duties assigned to the employee before). NET Tasks □ One-to-many with no inversionįirstly, let’s model this kind of relationship: One-to-many with no inversion – class diagram * “Task” would probably be a better name, but I didn’t want to make it confused with. Each employee has a list of his duties, whilst each single duty is assigned to only one employee. We are going to see it on the example of Employee and Duty* entities. In this post we’ll cover one-to-many with no reversion and one-to-many with reversion, as it also includes many-to-one relationship so you can have a comprehensive overview. We want both parent to know about its children, and each children to know about its parent. I will call it one-to-many with inversion. However in most cases what we’d like to have is a hybrid of one-to-many and many-to-one relationships. It means that, for instance, in many-to-one relationship, the one-end of it doesn’t have a reference to its children. I used a verb to know several times – so it’s time to explain it □ By “knowing” about the other end of a relationship I understand having a reference to it. In that case, many-end entity has a reference to its parent and knows about it, but the one-end entity doesn’t necessarily know about its children (at least not directly). On the other hand, the opposite relationship to one-to-many is many-to-one. One-to-many relationship means that the one-end entity knows about its children and many-end entity has a reference (foreign key) to its parent (but not necessarily knows about it). Classic examples are: bus and passengers, document and elements etc. One-to-many relationships are used in general for parent-children or whole-elements relations. In the 3rd post from SQLite-Net Extensions series we are covering the last type of relationship – one-to-many (and the opposite – many-to-one).
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