Here is a simplified version of my database model. I have two tables: "Image", and "HostingProvider" which look like this:
[Image]
id
filename
hostingprovider_id
[HostingProvider]
id
base_url
Image HostingproviderId is a many-to-one foreign key relationship to the HostingProvider table. (Each image has one hosting provider).
Essentially I want to be able to have my Image class look like this:
[Image]
Id
base_url
filename
In NHibernate, how can I create a mapping file that will combine the base_url from the HostingProvider table, into the Image class?
What you're looking for is this:
http://ayende.com/Blog/archive/2007/04/24/Multi-Table-Entities-in-NHibernate.aspx
Here's a peek of what it looks like:
<class name="Person">
<id name="Id" column="person_id" unsaved-value="0">
<generator class="native"/>
</id>
<property name="Name"/>
<property name="Sex"/>
<join table="address">
<key column="address_id"/>
<property name="Address"/>
<property name="Zip"/>
<property name="Country"/>
<property name="HomePhone"/>
<property name="BusinessPhone"/>
</join>
</class>
public class Image {
public virtual HostingProvider HostingProvider { get; set; } // NHibernate takes care of this
public virtual string BaseUrl { get { return HostingProvider.BaseUrl; } }
}
Related
I am trying to get this solved but can't so far. all kind of errors.
These are my db tables
Person (personID, name, age)
Role (roleID, roleName)
PersonRoles(personRolesID, personID, roleID)
this is my domain class
public Person
{
public virtual Roles RolesForThisPerson {get;set;}
public virtual string Name {get;set;}
public virtual int Age {get;set;}
}
public Roles
{
public virtual IList<string> RoleList {get;set;}
}
I am totally lost on how to approach this. I am so confused about sets, bags, lists... i don't even know where to start.
Anybody can give me a little push here?
thanks
Let's keep the DB schema as it is and adjust the C# domain classes first:
public class Person
{
public virtual string Name {get;set;}
public virtual int Age {get;set;}
public virtual IList<Role> RolesForThisPerson {get;set;}
}
public class Role
{
public virtual string RoleName { get; set; }
}
Now basic mapping for these two entities into defined tables:
<class name="Person" table="Person" lazy="true">
<id name="ID" column="personID">
<generator class="native" />
</id>
<property name="Name" not-null="true" />
<property name="Age" not-null="true" />
<!-- placeholder for roles -->
</class>
<class name="Role" table="Role" lazy="true">
<id name="ID" column="roleID">
<generator class="native" />
</id>
<property name="RoleName" not-null="true" />
</class>
And now we can use the <idbag> mapping and extend the Person class mapping this way:
<idbag name="RolesForThisPerson" batch-size="25" table="PersonRoles"
inverse="true" lazy="true" cascade="none" >
<collection-id column="personRolesID" type="System.Int32" >
<generator class="native" />
</collection-id>
<key column="personID" />
<many-to-many class="Role" column="roleID" />
</idbag>
The <idbag> can profit from the fact, that even the pair table has its own identifier. Cascade is set to none, expecting that roles are in the system, and users are only assigned to them (removed from). Attribute batch-size will effect how many SELECT statements will be executed when fetching the lazy roles collection.
I'm using <dynamic-component> elements to provide end-users the capacity to extend the functionality of our product by adding fields to the database.
A simplified version of our mapping is:
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="Caselle.Am0.DTO" assembly="Caselle.Am0.DTO" schema="dbo">
<class name="Asset" table="[tblAsset]" lazy="true">
<id name="ID" column="ID" type="Int32">
<generator class="native" />
</id>
<property name="AssetNumber" column="[AssetNumber]" type="long" not-null="true" />
<dynamic-component insert="true" update="true" name="UserDefinedFields" />
<many-to-one name="Classification" column="tblClassificationID" class="Lib.DTO.Classification, Lib.DTO" cascade="none" />
</class>
<class name="Classification" table="[tblClassification]" lazy="true">
<id name="ID" column="ID" type="Int32">
<generator class="native" />
</id>
<property name="Name" column="[Classification]" type="String" not-null="true" length="20" />
<dynamic-component insert="true" update="true" name="UserDefinedFields" />
<set name="Assets" table="tblAsset" lazy="true" cascade="all-delete-orphan" inverse="true">
<key column="tblClassificationID"/>
<one-to-many class="Lib.DTO.Asset, Lib.DTO"/>
</hibernate-mapping>
The classes look something like this:
public class Asset
{
public virtual long AssetNumber{get; set;}
public Classification Classification {get; set;}
public virtual IDictionary UserDefinedFields {get; set;}
}
public class Classification
{
public virtual string Name {get; set;}
public virtual ICollection<Asset> Assets {get; private set;}
public virtual IDictionary UserDefinedFields {get; set;}
}
The problem I'm running into is that now users want to use our filtering tools on their custom fields, and I get a QueryException(Could not resolve property 'X') when I run the following query:
var query = session.CreateCriteria<Asset>()
.Create Alias("c", "Classification")
.Add(Restrictions.Eq(Projections.Property("c.X"), "value")
.ToList<Asset>();
Is it possible to do this kind of a projection? How else might I write this query (I really like the Criteria API, since I'm generating this query on the fly, but if I have to work some other way...)?
I don't think you want to use the projection there. Try swapping out
.Add(Restrictions.Eq(Projections.Property("c.X"), "value")
for
.Add(Restrictions.Eq("c.UserDefinedFields.X", "value")
I have a problem with NHibernate. What i am trying to to is very simple:
I have two Classes. UserTicket and UserData. A UsertTicket has some UserData and a UserData belongs to one UserTicket:
public class UserData{
public virtual int Id { get; set; }
public virtual String PDF_Path { get; set; }
}
public class UserTicket
{
public virtual int Ticketnr { get; set; }
public virtual IList<UserData> UserData { get; set; }
}
And here the mappig xml:
<class name="UserTicket" table="UserTicket">
<id name="Ticketnr">
<generator class="identity"/>
</id>
<bag name="UserData" inverse="true" cascade="all-delete-orphan" lazy="false">
<key column="FK_Ticketnr" not-null="false"/>
<one-to-many class="UserData" />
</bag>
</class>
<class name="UserData" table="UserData">
<id name="Id">
<generator class="identity"/>
</id>
<property name="PDF_Path" />
</class>
When i run it, it works, but the column FK_Ticketnr in the DB-Table of UserData is always = NULL.
Someone told me i have to make a back link from my Child (UserData) to the Parent-Class. But i can not figure out how to do so. How do i get Hibernate to write the value of the Primary-Key (Ticketnr) of UserTicket into FK_Ticketnr?
Thanks in advance
Remove inverse="true" on your bag. That is telling NHibernate that the relationship is managed from the UserData mapping. Since you don't have a back reference, it is never persisted. The other option is to put a parent reference on UserData, but I wouldn't recommend it if you don't need it.
The alternative is the following...
public class UserData
{
// Keep your other properties, add this one too...
public virtual UserTicket Ticket { get; set; }
}
Modify your mapping file like this...
<class name="UserData" table="UserData">
<id name="Id">
<generator class="identity" />
</id>
<property name="PDF_Path" />
<many-to-one name="Ticket" column="FK_Ticketnr" />
</class>
Keep the inverse="true" on the bag.
If you go with this approach, you will need to set Ticket on your UserData objects when you add them to the UserData bag. In other words, you need to maintain both sides of the relationship. You could do this manually or you could try to automate it a little with with methods or constructors.
I am trying to create a table-per-hierarchy mapping using NHibernate 2.0.1.
I have a base class with properties that exist for each subclass that other classes inherit from. All of these objects are persisted to one table called Messages that contain all of the possible fields for each class. There is a SourceID which is the discriminator and should indicate which Poco to return for each subclass. Here is my current mapping.
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
assembly="NS.Core"
namespace="NS.Core.Model">
<class name="BaseMessage" table="Messages">
<id name="MessageID" type="Int64">
<column name="MessageID" />
<generator class="native" />
</id>
<discriminator column="SourceID" type="Int32"/>
<property name="DateCreated" access="property" column="DateCreated" type="DateTime" not-null="true"/>
<property name="DatePublished" access="property" column="DatePublished" type="DateTime"/>
<property name="SourceID" access="property" column="SourceID" type="Int32"/>
<many-to-one name="User" column="UserID" access="property" cascade="none" lazy="false" fetch="join" outer-join="true" />
<subclass name="NMessage" discriminator-value="0">
<property name="Body" access="property" column="Body" type="String"/>
</subclass>
<subclass name="BMessage" discriminator-value="1">
<property name="Title" access="property" column="Title" type="String"/>
<property name="Body" access="property" column="Body" type="String"/>
</subclass>
<subclass name="CMessage" discriminator-value="2">
<property name="Url" access="property" column="Url" type="String"/>
<property name="Body" access="property" column="Body" type="String"/>
</subclass>
</class>
</hibernate-mapping>
I get an error querying saying Could not format discriminator value to SQL string of entity NS.Core.Model.BaseMessage so I put a discriminator value on this class too althout it should never return the base class. That led me to some antlr errors.
Am I taking the wrong approach to this problem? I would like to query the table and get back a list of different POCOs that all inherit from the base class. It would never return the base class itself.
below is the BaseMessage.cs
using System;
using System.Collections.Generic;
using System.Runtime.Serialization;
using System.Text;
namespace NS.Core.Model
{
[Serializable]
[DataContract]
[KnownType(typeof(User))]
public class BaseMessage
{
#region Private variables
private long _messageID;
private DateTime? _dateCreated;
private DateTime? _datePublished;
private int _sourceID;
private User _user = new User();
#endregion
#region Properties
[DataMember]
public virtual long MessageID
{
get { return _messageID; }
set { this._messageID = value; }
}
[DataMember]
public virtual DateTime? DateCreated
{
get { return _dateCreated; }
set { this._dateCreated = value; }
}
[DataMember]
public virtual DateTime? DatePublished
{
get { return _datePublished; }
set { this._datePublished = value; }
}
[DataMember]
public virtual int SourceID
{
get { return _sourceID; }
set { this._sourceID = value; }
}
[DataMember]
public virtual User User
{
get
{
if (this._user != null)
{ return this._user; }
else { return new User(); }
}
set { this._user = value; }
}
#endregion
}
}
The approach is sound. I have done exactly this several times.
You could make it explicit in your code my having BaseMessage's default constructor be protected.
You need to declare a discriminator-value on the base class as well.
I favor string values for discriminators, as this clearer when performing SQL queries or reports. Also, since instances of BaseMessage shoudl not exist, in would use null for its discriminator value.
<class name="BaseMessage" table="Messages" discriminator-value="null">
<id />
<discriminator column="SourceID" />
<subclass name="NMessage" discriminator-value="NMessage">
</subclass>
<subclass name="BMessage" discriminator-value="BMessage">
</subclass>
<subclass name="CMessage" discriminator-value="CMessage">
</subclass>
</class>
Also, I see that you have mapped a property to the discriminator column. You should instead have a method that returns something unique to the class - in this case the code.
Note that you cannot change the class of a mapped entity after it has been saved. Not even by changing the discriminator. If you did change it via SQL, your 2nd level cache will still hold a version with the original class.
class BaseMessage
{
public virtual string MessageType { return null; }
}
class NMessage : BaseMessage
{
public override string MessageType { return "NMessage"; }
}
Finally, your mapping file is overly verbose as it includes values which are the default. The following attributes and elements can be removed:
access="property" - this is the default
type="String" - all the types you use can be inferred from your .NET class
column="COL" - default is the same as the name
similarly for the id column element
All of your Message subclasses have property Body, so move it to the base class mapping. If this field can be longer than your database varchar, it should be a text column and have type="StringCLob" which maps to string in .NET
<class name="BaseMessage" table="Messages" discriminator-value="null">
<id name="MessageID">
<generator class="native" />
</id>
<discriminator column="SourceID"/>
<property name="DateCreated" />
<property name="DatePublished" />
<many-to-one name="User" column="UserID" cascade="none" lazy="false" fetch="join" outer-join="true" />
<property name="Body" type="StringCLob" />
<subclass name="NMessage" discriminator-value="NMessage">
</subclass>
<subclass name="BMessage" discriminator-value="BMessage">
<property name="Title" />
</subclass>
<subclass name="CMessage" discriminator-value="CMessage">
<property name="Url" />
</subclass>
</class>
I'm currently trying to solve a problem. I have a class table inheritance aka table-er-subclass (one main table + several others with additional data). In my app both base object instances and extended objects can exist. Now I want to be able to sometimes fetch only those base objects and sometimes both types. A simple example (both classes are mapped with all of their properties)
public class Base
{
public in ID {get; set;}
public string Something {get; set;}
}
public class Extended : Base
{
public bool NewProp{get; set;}
}
now running hql query "from Base" would fetch both Base and Extedned objects. Is there any way to restrict such behavior to fetch only Base objects?
with HQL you should be able to use the "class" special property:
from Base b where b.class=Base
another approach could be to use plain SQL where you have greater control of what you retrieve.
Anyway check the (N)Hibernate docs.
That's the mapping for the above sample (if there's any error forgive me it must be a typo cause the sample runs)
<?xml version="1.0" encoding="utf-8"?>
<hibernate-mapping auto-import="true"
default-lazy="false"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="urn:nhibernate-mapping-2.2">
<class name="Base, Test"
table="base">
<id name="ID"
access="property"
column="ID"
type="Int64"
unsaved-value="0">
<generator class="sequence">
<param name="sequence">base_id_seq</param>
</generator>
</id>
<property name="Something"
access="property"
type="String">
<column name="somethin"/>
<joined-subclass name="Extended, Test"
table="extended"
schema="extended">
<key column="id" />
<property name="NewProp"
access="property"
type="Boolean">
<column name="newProp"/>
</property>
</joined-subclass>
</class>
</hibernate-mapping>