Filling the program array with rows

This topic describes how to fill a program array for a tree-view.

Once the program array is defined based on the screen-array definition of the tree-view table, fill the array with the tree-view definition.

You can directly fill the program array before the dialog execution. Once the dialog has started, you must use the methods DIALOG.insertNode(), DIALOG.appendNode() and DIALOG.deleteNode(), if you want to modify the tree, otherwise information like multi-range selection flags and cell attributes will not be synchronized.

Fill the rows in the correct order defining the structure of the tree, to reflect the parent/child relationship of the tree nodes. If a row defines a tree-view node with a parent identifier that does not exist, or if the child row is inserted under the wrong parent row, the orphan row will become a new node at the root of the tree.

In order to fill the program array with database rows defining the tree structure, you will need to write a recursive function, keeping track of the current level of the nodes to be created for a given parent.

The next example shows how to fill the array with data coming from a database table having the following structure:

CREATE TABLE dbtree (
     id SERIAL NOT NULL,
     parentid INTEGER NOT NULL,
     name VARCHAR(20) NOT NULL
   )

The difficulty with fetching a tree from a database table is in the cursor management, which can not be used recursively. A workaround for this problem is to fetch all the children of a given node at once, then call the function recursively for each of the fetched nodes:

TYPE tree_t RECORD
       id INTEGER,
       parentid INTEGER,
       name VARCHAR(20)
    END RECORD

DEFINE tree_arr tree_t 

FUNCTION fetch_tree(pid)
    DEFINE pid, i, j, n INTEGER
    DEFINE a DYNAMIC ARRAY OF tree_t 
    DEFINE t tree_t 
   
    DECLARE cu1 CURSOR FOR SELECT * FROM dbtree WHERE parentid = pid 
    LET n = 0
    FOREACH cu1 INTO t.*
       LET n = n + 1
       LET a[n].* = t.*
    END FOREACH

    FOR i = 1 TO n 
        LET j = tree_arr.getLength() + 1
        LET tree_arr[j].name = a[i].name 
        LET tree_arr[j].id = a[i].id 
        LET tree_arr[j].parentid = a[i].parentid 
        CALL fetch_tree(a[i].id)
    END FOR

END FUNCTION