Multiple one to many relation to the same table | The catchsomeair.us Forums
Mar 12, The NHibernate mapping would look similar, with catchsomeair.usMany() mapping on one or both sides of the relationship. From the Course and and explicitness. ← Efficient querying with LINQ, AutoMapper and Future queries. Feb 4, To. Use commas to separate multiple email addresses NHibernate stores the mapping information in XML format catchsomeair.us files -- you should have catchsomeair.us file for each entity class. catchsomeair.us file It provides a Fluent API also enables you to use LINQ to query data on top of the NHibernate engine. In the. Jun 9, But even then, I would probably prefer some lightweight mapping library It will surface any edge cases in NHibernate's LINQ support much One more reason not to abstract NHibernate decimal mostExpensiveProduct = session. A long- standing issue that has caused a lot of confusion in many of my.
You will notice that we have 3 groups of statements. The first one will insert the customer, and that customer's ID is the Guid, which is highlighted.
Chapter 6. Collection Mapping
The second statement is insert into the orders table. You will notice the same Customer Id Guid is set in there, so have that foreign key set. The last statement is the update, which will update the foreign key to the same customer id once again.
Now the problem is that the customer has the orders, and the orders has the customer, there's no way that we haven't told NHibernate that it's actually the same relationship.
The way we do this is with inverse equals true. So let's go to our customer. If we look at how those are inserted, we get the insert in the customer, and the insert into orders, but we don't have that duplicate update of the foreign key because it's being updated when the orders are being saved. Now, you should note that if you only have a unidirectional association and it's the set that is maintaining this relationship, then if you turn inverse equals true, that foreign key is never going to be set, and those items are never going to have their foreign keys set in the database.
If you look at the many-to-one relationship in the Order. There are quite a range of mappings that can be generated for collections, covering many common relational models. We suggest you experiment with the schema generation tool to get a feeling for how various mapping declarations translate to database tables. Mapping a Collection The NHibernate mapping element used for mapping a collection depends upon the type of interface. It is not used for one-to-many associations.
It is useful if the collection should contain only a subset of the available data. For one to many associations, you may want to disable this setting. This allows for minor performance optimization in some cases.
This is useful if you want to have a view instead of a base table. This attribute is obsoleted in favor of fetch. It has no value matching the subselect fetch value. Otherwise NHibernate will use reflection to determine the element type to use. The mapping of an IList or array requires a separate table column holding the array or list index the i in foo[i].
NHibernate - Inverse Relationships
If your relational model doesn't have an index column, use an unordered ISet instead. This seems to put people off who assume that IList should just be a more convenient way of accessing an unordered collection. IList elements don't just spontaneously rearrange themselves! On the other hand, people who planned to use the IList to emulate bag semantics have a legitimate grievance here.
A bag is an unordered, unindexed collection which may contain the same element multiple times. Note that bag semantics are not really part of the ICollection contract and they actually conflict with the semantics of the IList contract however, you can sort the bag arbitrarily, discussed later in this chapter. NHibernate can't create, delete or update rows individually, because there is no key that may be used to identify an individual row.
Collection foreign keys Collection instances are distinguished in the database by the foreign key of the entity that owns the collection. This foreign key is referred to as the collection key column, or columns, of the collection table. There can be a nullability constraint on the foreign key column. For most collections, this is implied. Collection elements Collections can contain almost any other NHibernate type, including: This is an important distinction.
An object in a collection might be handled with "value" semantics its life cycle fully depends on the collection owneror it might be a reference to another entity with its own life cycle. In the latter case, only the "link" between the two objects is considered to be a state held by the collection.
How to get the best performance out of NHibernate (and when not to use it at all)
The contained type is referred to as the collection element type. The first two map elements with value semantics, the next two are used to map entity associations.
Indexed collections All collection mappings, except those with set and bag semantics, need an index column in the collection table. An index column is a column that maps to an array index, or IList index, or IDictionary key. The mapped column contains sequential integers that are numbered from zero by default.Hibernate Tutorial 14 - One To Many Mapping
If the type takes a length and does not already specify it, its length. Make sure you override GetHashCode and Equals correctly on the component class. A bag does not retain its order when it is retrieved from the database, but it can be optionally sorted or ordered.
Also consider using an ISet as the property type. Collections of Values and Many-To-Many Associations Any collection of values or many-to-many associations requires a dedicated collection table with a foreign key column or columnscollection element column or columns, and possibly an index column or columns.
This is a special case; disabling laziness of the collection itself only would only eagerly load the list of ids of the associated entities. If not specified, the primary key of the associated class is used. We will first create a new application in which we will create some relationships among the customer and order entities. The first relationship we're going to look at is a classic collection relationship.
We have a customer with a collection of orders.
This is a one-to-many relationship and it's represented in the database by 2 tables and there is a customer ID on the orders table and we have a foreign key relationship back to the customer. First we need to create a database and two tables Customer and Order. The following image shows the Customer Table. The following image shows the Order Table in which you can see the foreign key relationship back to the customer. We need to define the connection string in the app. Here is the Customer. Add order ; order.