com.smartgwt.client.docs
Interface TreeDataBinding

public interface TreeDataBinding

Tree DataBinding

The Smart GWT TreeGrid component is a visual representation of a tree and requires a Tree or ResultTree datatype passed via the data attribute to initialize the tree view. The Tree datatype is used when you want to provide all of the tree nodes in one shot at initialization time. The ResultTree datatype is used when you want portions of the tree to be loaded on demand from the server.

Providing all data to the Tree at creation

The simplest mechanism by which to initialize a Tree is to simply provide all the data up-front when the Tree itself is created. Depending on the format of your tree data, this can be done by setting root or data. This functionality is provided by the Tree class.

For examples of this type of databinding, see the following SDK examples:

• TreeGrid Initialization Example

Loading Tree nodes on demand

In this mode, tree nodes are loaded on-demand the first time a user expands a folder. This approach is necessary for large trees. This functionality is provided by the ResultTree class, which uses a DataSource to load data from the server. Each DataSource Record becomes a TreeNode.

ResultTrees require that every node in the tree have an id that is unique tree-wide. When the user expands a folder whose contents have not yet been loaded from the server (or you programmatically call openFolder() on such a node), the client automatically sends a DSRequest to the server to ask for all immediate children of that node. The DSRequest criteria will specify the id of the node for which children are being requested via the parentId property (see parentIdField). This client is asking the server: "give me all nodes whose parentId is the id of this node".

If there are no pre-existing node ids in the dataset you are loading, you must generate node ids (because the client needs some way to identify nodes when talking to the server). Generally a node id should contain whatever information is required to fetch the node and it's children on the server. One typical approach is to use the path to the node as a node id. For XML datasets in particular, the path may be a valid XPath, so that server-side lookup of child nodes is just a matter of applying the node id as an XPath to a server-side XMLDocument.

ResultTrees are created for you by the TreeGrid when you set dataSource, but you can pass an initial dataset to a databound TreeGrid by setting initialData. The idField is derived from the dataSource you provide to the TreeGrid - the first field marked as primaryKey:true becomes the idField of the ResultTree. The parentIdField is found by looking for a field that has a foreignKey property pointing to the idField.

If you do not provide initialData, the first DSRequest you receive will be a request for the nodes under root. The id of the root node of the tree is the value of the rootValue attribute on the parentIdField of the Tree DataSource.

For examples of this type of databinding, see the following SDK examples:

• TreeGrid DataBinding Example

Multi-Level load on demand

The ResultTree's DSRequests ask for the immediate children of a node only (by specifying parentId in the criteria). Any nodes returned whose parentId field value is unset or matches this criterion will be added to the tree as immediate children of the node. However you are also free to return multiple levels of children. This can be done by simply returning a flat list of descendents with valid id's and parentId's, exactly as though you were initializing a multi-level tree via data.

Note that when receiving multiple levels of children, the ResultTree's assumption is that if any children are loaded for a parent, then that parent is considered fully loaded.

When loading children for a given parent node, the ResultTree calls DataSource.fetchData on its DataSource. For custom code that may need to reference the parentNode or tree in some way, the parent node whose children are being loaded is available on the dsRequest instance in the DataSource flow as dsRequest.parentNode, where it can be inspected during DataSource.transformRequest.