Now suppose that you are retrieving an Order instance or a bunch of them, doesn't really matter and you don't instruct NHibernate to already fetch the Customer or Employee data.
You haven't requested the Customer or Employee data, so it shouldn't be there, right? But it shouldn't be null either, right? So NHibernate assigns an instance of the CustomerProxyType class to the Customer property, and an instance of EmployeeProxyType and initializes both proxies so that they contain their identifier value, which you already have in memory anyway after selecting the order record.
You can safely use the Order instance s and you can even access the Employee and Customer instances and nothing will happen. But, whenever you access any of the non-identifier members that means properties and methods of a proxy instance, NHibernate needs to make sure that the data of either the Customer or the Employee depending on which one you're using needs to be fetched from the database. So how does NHibernate do that? The proxies will override all of your properties and methods and when one of them is accessed, NHibernate will either fetch the data of the entity if it's not present yet and then proceed with the original implementation of the property or the method, or it will immediately call the original implementation if the data was already present.
This is basic OO In order to do that, NHibernate needs to override every public member to make sure that this extra behavior is triggered at the appropriate time. Now, there are quite a few people who dislike this requirement. First of all, there is a minor performance cost to calling virtual members as opposed to calling non virtual members.
However, this performance cost is really extremely small and in practically every situation it's completely negligible. This extra cost certainly doesn't even compare to some real world performance costs, like hitting the database more often than you should or retrieving more data than you really need. You can leave it off and let NHibernate keep track of object identifiers internally. However, for many applications it is still a good and very popular design decision.
What's more, some functionality is available only to classes which declare an identifier property:. We recommend you declare consistently-named identifier properties on persistent classes. A central feature of NHibernate, proxies , depends upon the persistent class being non-sealed and all its public methods, properties and events declared as virtual.
Another possibility is for the class to implement an interface that declares all public members. You can persist sealed classes that do not implement an interface and don't have virtual members with NHibernate, but you won't be able to use proxies - which will limit your options for performance tuning. A subclass must also observe the first and second rules. It inherits its identifier property from Cat. You have to override the Equals and GetHashCode methods if you intend to mix objects of persistent classes e.
Even if both objecs a and b are the same database row they have the same primary key value as their identifier , we can't guarantee that they are the same object instance outside of a particular ISession context. If the value is the same, both must be the same database row, they are therefore equal if both are added to an ISet , we will only have one element in the ISet. Unfortunately, we can't use that approach.
NHibernate will only assign identifier values to objects that are persistent, a newly created instance will not have any identifier value! Business key equality means that the Equals method compares only the properties that form the business key, a key that would identify our instance in the real world a natural candidate key :. Keep in mind that our candidate key in this case a composite of name and birthday has to be only valid for a particular comparison operation maybe even only in a single use case.
Is it mandatory? No Is the above code correct? Yes Can we do something before you call the parent's constructor? You can do it in any order you please. FluentConfiguration ; nhvConfiguration. Register Assembly. Load "Business. GetEngine ; validatorEngine. Configure nhvConfiguration ; ValidatorInitializer. Problem of Granularity: We can have more classes than database tables. Problem of Inheritance: A database does not support inheritance. Problem of Impedance mismatch: The mismatch between structural and data type representation in classes and databases.
Impedance mismatch For example, consider the following class with properties and Employee table with column and data type: It is clear from the preceding example that they differ in structure and data type representations we will review in more detail in later series.
Now we can say that using Hibernate we can map each and every property of the Class with the relational table. NHibernate does all the database work. Eliminates the necessity to write SQL statements or create a stored query. We can have all of our data access logic contained within our application. Data Cartography, not only will our queries be effective, but they will also be validated by the compiler.
Therefore, if our underlying table structure changes, the compiler will alert us that we need to change our queries! As source code from the GitHub repository. As a downloadable Zip package from SourceForge. The stable format can be download as: NHibernate GA-bin: Zip file format NHibernate How to retrieve data in a web page that was data-bound to a collection of NHibernate objects, all without any code-behind or other additional code.
A basic NHibernate project is divided into major parts. Hibernate Configuration File: hibernate. But a basic NHibernate project is composed of the following three major parts.
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