To store your HopObjects into a relational database system you need to define a database mapping. This is done in the type.properties files located in the persistent HopObject's prototype directory (e.g. apps/myApp/MyPrototype). The type.properties files contain no JDBC connection information, which is located in the db.properties file in the Helma installation directory or in the application directory.
_db = datasourceName
The _db entry describes the database source to use for managing objects of this type. datasourcename is the connection's name defined in the db.properties, which is located in Helma’s installation directory or the application directory. The db.properties file contains information about the JDBC connections, like the JDBC driver, the connection URL and the database username and password.
_table = TABLENAME
The _table entry tells Helma which table to use for objects of this type within the database. To avoid problems with reserved words of SQL or your database system you should prefix your table names. (e.g. T_Story for the Story prototype’s table)
Extended prototypes are usually stored in the same relational database table. Thus, Helma needs a way to tell which row in the table should be instantiated with which object prototype. This is done using the _prototype entry, specifying a column in the table containing the name of the prototype for each row.
_prototype = PROTOTYPE_COLUMN_NAME
This picture shows a database table where Animals and Dogs could be stored. A Dog is a sub-prototype of the Animal prototype. It inherits every property from the Animal and defines two new properties called "Breed" and "Color".
Note: The Dog’s type.properties just defines the two new properties. All other stuff will be inherited from the Animal.
_extensionId = String or Integer
If you extend a prototype, Helma will use the name of the sub-prototype as value for the _prototype database column. This could slow down the performance. Better would be to choose a numeric value, which result faster index retrievals and queries. You can define this numeric value in the _extensionId property of the sub-prototype.
Example: If Helma needs all cats, the db-layer can filter all animals with the value '260486'. The value '260486' is defined in the cat’s type.properties as _extensionId! For dogs the _extensionId is set to a 'dogu dugu' string. Animals’ type.properties defines no _extensionId, so Helma uses the prototype’s name, which is 'Animal'!
Download the animal demo application:
_name = NAME_COLUMN
The optional _name entry tells Helma which database column to use as object name. This is important for the user prototype, since it defines which column constitutes the user name. This field is only used by the session.login(name, pw)/app.registerUser(name, pw) functionality!
_extends = Prototype
The _extends entry engages Helma to inherit properties, functions and skins from another prototype. This can be compared to Java’s subclassing mechanism.
For example could be a Dog's _extends value the Animal, which inherits to the Dog prototype basic properties like father or mother, some skins and standard functions like getBiologicalClassification()
_id = primaryKeyColumnName
The _id entry defines the column to use as primary key. Helma requires a single primary key with no other functionality. You can read this unique ID from the _id-property of the HopObject.
_parent = localPropertyName, localProperty.parentsCollectionName, root.collectionName
The _parent entry contains a comma-separated list of properties of objects of this type to be used as parent. Objects must know their parent in order to generate correct URLs in their href() function. If a property in the list is null, Helma will look on the following one to fetch a parent object.
If an entry in the _parent item does not contain a dot, it is interpreted as an object property of the current object that acts as the object's parent. If an entry contains a dot character, the part after the dot is interpreted as a collection in the parent object in which the current object is contained. Alternatively or additionally, a second or third dot separated part may indicate an object reference instead or in addition to a collection or mountpoint. If the _parent is specified as "root", it is not interpreted as a property of the current object. Instead, the application's root object is used as parent object.
The _parent entry solves a very specific problem: HopObjects do not know their canonical URLs if you call the href() function, since they can be members of more than one collection.
Example: James Nachtwey, Steve McCurry and Annie Leibovitz are well known photographers. A photographer might work for an agency, so the photographer’s prototype contains a property acency, but if they don’t, it’s null. Nachtwey and McCurry are war photographers, so a root.warphotographers collection cointains both. Leibovitz is neither taking pictures in war zones, nore working for an agency. All photographers are stored in the root’s photographers collection.
The Photographer's types.properties looks like that:
_parent = root.warphotographers, agency, root.photographers
agency = object(Agency)
Helma’s href() will look first in the war photographers collection and return an URL like /warphotographers/nachtwey, if the person is member of this. Now you call href() on the object Annie Leibovitz. She isn’t member of warphotographers, her agency property is null, but she is member of root.photographers, so href() will return /photographers/leibovitz.
_children = collection(SomeHopObject)
It is used to define a HopObject itself as a collection. The keyword _children acts like a normal property, so you can use all of the collection specifications (.local, .foreign, .accessname, etc.) when defining the collection.
The property naming is case sensitive since Helma 1.7. This means that obj.foo, obj.Foo and obj.FOO no longer point to the same property. Properties starting with '_' are not persistable! If you define a property like '_lastAccess', Helma will not map it to a database column, even if you define a mapping.
simplePropertyName = DB_COLUMN_NAME
A simple property maps a property name of the object to a column of the database table. The type of the table's column need not be specified. Helma does all necessary conversion when reading or writing a property value.
simplePropertyName.readonly = true
Initializes the property with the value from the database and will not propagate updates on this property to the database. Please note that the property still can be modified by the application but all changes will be lost after restarting the application or reloading it's value from the database. If you need to prevent any modification on a property, you have to provide a setter function for it.
simplePropertyName.private = true
The private flag forces Helma to update this column only in the database, but prevents any updates on collections and references containing the modified object.
obj = object(SomeHopObject)
coll = collection(SomeHopObject)
moutpointName = mountpoint(SomeTransientHopObject)