I have a table A that has a references to a table B through a third table C. C contains the primary key of A and B. For each A there is at most one record in C. When I try to create a mapping for A such that I am referencing B, I use the References function, but it does not allow me to specify that the mapping goes through another table and not directly. What is the proper way to do that?
The only mapping that I know that could do that would be a HasManyToMany in the mapping of A :
HasManyToMany(x => x.B)
.WithTableName("C")
.WithParentKeyColumn("A_Id")
.WithChildKeyColumn("B_Id");
The problem is that the mapping is for A having a list of Bs, not just one. I don't know how you could do it to get only one in a clean way.
I believe I have found the answer in google code samples. In the mapping class, it is possible to write an additional:
WithTable("SomeTable", c => { c.Map(x => x.Col1); });
Related
I have 3 tables that represents a many to many mapping.
Two tables with different ids and a third table with a composite key referencing the other two.
How can i map this using the classmap in nhibernate?
The following doesn´t work:
HasManyToMany(m =>
m.ListBlockStatus)
.Table("BlockTypeAction")
.ParentKeyColumn("IdBlockActionDefinition")
.ChildKeyColumn("IdBlockTypeCategory")
.Table("BlockTypeCategory")
.ParentKeyColumn("Id");
Found what i need, unfortunately the query in the end is not an inner join.
HasManyToMany(m => m.ListBlockStatus)
.Table("BlockTypeAction")
.ChildKeyColumns.Add("IdBlockActionDefinition")
.ParentKeyColumn("IdBlockTypeCategory")
.Cascade.All();
I'm working with a legacy database put together by some very strange people. I'm writing an NHibernate DAL over the top of it but running into some odd mapping scenarios.
In one example, I have a table with a number of fields including LE_RECNUM (integer primary key) and LE_CODE (string).
However, all relationships throughout the database join onto LE_CODE, not LE_RECNUM, for some unfathomable reason.
I need to specify that LE_RECNUM is the Id in my mapping file, because I need the primary key to be generated when I insert records. However, I want all associations to use LE_CODE instead of LE_RECNUM.
Can anyone suggest how I might do this?
References(x => x.SomeProperty).Column("LE_CODE").PropertyRef(x => x.SomePropertyInParent);
In order to use my Fluent NHibernate mappings on SQL Azure, I need to have a clustered index on every table. The default heap tables that Fluent NHibernate creates for many-to-many joins obviously don't do this as they don't have primary keys.
I want to be able to tell one side of the relationship to create a clustered index for its join table, but I'm not sure how. Here's what my mappings look like:
public class UserMap : ClassMap<User>{
public UserMap()
{
Table("Users");
Id(x => x.UserId).GeneratedBy.Identity().Column("UserId");
Map(x => x.UserName).Unique().Not.Nullable().Length(DataConstants.UserNameLength).Column("UserName");
Map(x => x.Email).Unique().Not.Nullable().Length(DataConstants.EmailAddressLength).Column("Email");
Map(x => x.Password).Not.Nullable().Length(DataConstants.PasswordHashLength).Column("Password");
HasMany(x => x.Clicks).Cascade.AllDeleteOrphan();
HasManyToMany(x => x.Roles).Cascade.SaveUpdate().Table("UsersInRole").ParentKeyColumn("UserId").
ChildKeyColumn("RoleId");
}
}
Please let me know if you need any more information!
I don't know if Fluent supports it directly (if not, just include the xml), but you can do it with Auxiliary Database Objects
<nhibernate-mapping>
<database-object>
<create>create clustered index ix on UsersInRole(UserId, RoleId)</create>
<drop>drop index UsersInRole.ix</drop>
</database-object>
</nhibernate-mapping>
I struggled with the same problem as the topic starter (as I'm combining Fluent NHibernate and Sql Azure as well) but the given answer didn't satify. This is because it is not dynamic by convention. Of course the HBM file could be dynamically created and added to the configuration afterwards with configuration.AddXmlFile("AddClusteredIndexesToManyToManyTables.hbm.xml"); but I just don't like the HBM files and I can't imagine there is a better way.
After several hours I found another solution which is dynamic (and readable!) and does not deal with hbm xml files. The solution is as follows:
Assumption #1: I will create a composite primary key for each junction table that results in a clustered index in SQL Server.
After the configuration has been build (thus the mappings are parsed), (Fluent) NHibernate gives us the oppertunity to look into the actual mappings with configuration.ClassMappings and configuration.CollectionMappings. The latter is used because we are interested in the many-to-many mappings.
foreach (var collectionMapping in configuration.CollectionMappings
// Filter on many-to-many
.Where(x => !x.IsOneToMany)) {
// Build the columns (in a hacky way...)
const string columnFormat = "{0}_id";
var leftColumn = new Column(string.Format(
columnFormat,
collectionMapping.Owner.MappedClass.Name));
var rightColumn = new Column(string.Format(
columnFormat,
collectionMapping.GenericArguments[0].Name));
// Fetch the actual table of the many-to-many collection
var manyToManyTable = collectionMapping.CollectionTable;
// Shorten the name just like NHibernate does
var shortTableName = (manyToManyTable.Name.Length <= 8)
? manyToManyTable.Name
: manyToManyTable.Name.Substring(0, 8);
// Create the primary key and add the columns
var primaryKey = new PrimaryKey {
Name = string.Format("PK_{0}", shortTableName),
};
primaryKey.AddColumn(leftColumn);
primaryKey.AddColumn(rightColumn);
// Set the primary key to the junction table
manyToManyTable.PrimaryKey = primaryKey;
}
And yes, the logic to get the left and right hand columnsAfter that the columns are a bit hacky but it works and you are free to adjust and edit my solution (^_-). The problem is that the collection mapping is fairly empty/unfilled.
Good luck with coding and creating conventions!
Any set of column(s) can be a clustered index... there is no requirement that I know of which forces you to use a PK constraint in order to build a clustered index.
More over I do not understand how a client could REQUIRE a clustered index. It might make them as a default but that's different than require. This is often reported as a "best practice" for SQL Server, but to the client, there's no real distinction between a secondary b-tree index on a column and the clustered index which orders the table's record. How would the client be able to distinguish the underlying storage of the data? One stores the data ordered by the cluster key, the other doesn't.
Maybe fluent-nhibernate performs better, or claims to - but it will "work" without any indexes.
But I'm not an expert in either so YMMV.
Great solution M.Mimpen.
When need map interfaces, put the ChildKeyColumn with interface name.
Ex:
HasManyToMany(x => x.Acessos).("IRole_id");
The class Acesso implements IRole interface. If you don´t inform child key name, the column created will be "Acesso_id", but when create the key will try "IRole_id".
I want to create a many to many relationship, but I want to have in the new table(MessageReceivers) a unique contraint on both columns (AdvanceMessageId,UserId):
mapping.HasManyToMany(x => x.Receivers)
.WithParentKeyColumn("AdvanceMessageId")
.WithChildKeyColumn("UserId")
.Cascade.All()
.LazyLoad()
.WithTableName("MessageReceivers");
Thanks for help
Old post... but in case someone else arrives here looking for the answer:
You need to add .AsSet() to the HasManyToMany mapping definintion.
i.e.
mapping.HasManyToMany(x => x.Users)
.WithTableName("MessageReceivers")
.WithParentKeyColumn("UserId")
.WithChildKeyColumn("AdvanceMessageId")
.Inverse().AsSet();
This will setup an unique, composite primary key constraint on the link table that uses both columns.
(clustered index)
The down side is AsSet() cannont be used with collection properties of type IList, so no for loops without casting.
I have been using ICollection and instantiating them as HashSet for my applications and it works well.
More info on collection management with Fluent Nhibernate:
List: Ordered collection of entities, duplicate allowed. Use a .net IList in code. The index column will need to be mapped in NHibernate.
Set: Unordered collection of unique entities, duplicates not allowed. Use Iesi.Collection.ISet in code. It is important to override GetHashCode and Equals to indicate the business definition of duplicate. Can be sorted by defining a orderby or by defining a comparer resulting in a SortedSet result.
Bag: Unordered list of entities, duplicates allowed. Use a .net IList in code. The index column of the list is not mapped and not honored by NHibernate.
You should also map the inverse side of the relationship like
mapping.HasManyToMany(x => x.Users)
.WithTableName("MessageReceivers")
.WithParentKeyColumn("UserId")
.WithChildKeyColumn("AdvanceMessageId")
.Inverse();
In newest Fluent NHibernate you will have to change
WithTableName -> Table
WithParentKeyColumn -> ParentKeyColumn
WithChildKeyColumn -> ChildKeyColumn
I am trying to create a mapping to a database table that has no primary keys/references.
public class TestMap : ClassMap<<Test>Test> {
public TestMap() {
WithTable("TestTable");
Map(x => x.TestColumn);
}
}
This fails and expects id or composite-id. Is this possible in fluent nhibernate?
In Oracle at least, I have used "ROWID" for this. For mssql you might use the "ROW_NUMBER()" builtin function for readonly access to the table, but I haven't tried that...
No. You'll have to add a surrogate primary key, such as an identity column in SQL Server, to map this table. As far as I know, this isn't supported by NHibernate itself.
Why don't you have a primary key on this table?
This functionality isn't supported by nhibernate as far as I know. As a general rule of thumb, however, you should really always have some kind of ID and if you find yourself in a situation where you think you don't need one you should assess your data model. An ID, whether it be a table-specific primary key, or a surrogate key from another table, should exist. This not only ensures that nhibernate can process the table, but helps performance via indexing.
Before you start assuming nhibernate isn't going to fulfill your needs, consider why you don't have a key on the table and what kind of sense it makes not to have one.
If we can bring a column from table having no primary key/identity coulmn, then we can use fluent as below:
Id(x => x.TempID).Column("TempID");
If the table contains data that belongs to another entity, you could map it as a collection of components. Components are not identified by themselves, but they belong to another entity, which is identified.
You can map an entity to a table without keys defined in the database. I do so in legacy SQL Server databases. However, the table must have a candidate key (some set of columns that actually stores a unique combination of values). The concept of entity involves the notion of some kind of identity.
Instead of this, what you're trying in your code is to map an entity without identity, wich isn't possible.