Data Binding¶

Entry_Item binds data-aware controls and columns to Data Dictionary fields. Legacy code often used global table-buffer field names like Customer.Name; TechStack code binds through the Data Dictionary object that owns the local buffer, such as oCustomerDD.Name or oCustomer_DD.Name. Entities define the fields, while Data Dictionaries own the local record buffer used by the UI.

See the DEO Binding API reference for binding and server protocol members.

Before: global table buffer binding¶

WebOrder-style code can define a Data Dictionary object and set it as Main_DD and Server, while Entry_Item still names the global Table.Field buffer.

Object oCustomerDataDictionary is a cCustomerDataDictionary
End_Object

Set Main_DD to oCustomerDataDictionary
Set Server  to oCustomerDataDictionary

Object oCustomerName is a cWebForm
    Entry_Item Customer.Name
    Set psLabel to "Name:"
End_Object

Customer.Name names the global Customer table buffer; it does not name the oCustomerDataDictionary object.

Now: local Data Dictionary object binding¶

TechStack binding names the Data Dictionary object before the dot. The object owns the local buffer used by the control or column.

Object oCustomerDD is a cCustomerDataDictionary
End_Object

Set Main_DD to oCustomerDD
Set Server  to oCustomerDD

Object oCustomerName is a cWebForm
    Entry_Item oCustomerDD.Name
    Set psLabel to "Name:"
End_Object

oCustomerDD and oCustomer_DD are ordinary object names; the important part is that the prefix is the Data Dictionary object, not the table name.

Object oRoomDD is a cRoomDataDictionary
End_Object

Set Main_DD to oRoomDD
Set Server to oRoomDD

Object oRoomDD_Name is a cWebForm
    Set psLabel to "Name"
    Entry_Item oRoomDD.Name
End_Object

This is the same binding shape as oCustomerDD.Name: oRoomDD is the Data Dictionary object and Name is the field.

Migration pattern¶

• Keep the field suffix after the dot.
• Replace the table name before the dot with the DD object name that owns that table's local buffer.
• If the local object uses another naming style, use that exact object name, e.g. oCustomer_DD.Name.

Related Data Dictionaries¶

For parent or related fields, connect related Data Dictionary objects with Set DDO_Server, then bind each field through the Data Dictionary object that owns that local buffer.

Object oRoom_DD is a cRoomDataDictionary
End_Object

Object oPresenter_DD is a cPresenterDataDictionary
End_Object

Object oPresentation_DD is a cPresentationDataDictionary
    Set DDO_Server to oRoom_DD
    Set DDO_Server to oPresenter_DD
End_Object

Set Main_DD to oPresentation_DD
Set Server to oPresentation_DD

Entry_Item oPresentation_DD.Title
Entry_Item oRoom_DD.Name
Entry_Item oPresenter_DD.FirstName

The prefix before the dot chooses the local buffer owner; it is not a global table selector.

Calculated and back-end values¶

Binding is not limited to stored fields. A bound value can also be computed by the storage back end and returned alongside stored fields.

cDbQuery.Bind_Native_Expression adds a back-end-specific expression as an extra column in an ad hoc query result, next to the fields added with Entry_Item. The expression string is passed to the back end, so its syntax is back-end specific (the example below uses SQLite string concatenation).

Object oCustomerQuery is a cDbQuery
    Set Server to oCustomer_DD

    Entry_Item oCustomer_DD.Name
    Send Bind_Native_Expression "Name || ', ' || City" (RefTable(oCustomer_DD.Name))
End_Object

Variant[][] aRows
DbRowId[] aRowIds
Get FetchFirst of oCustomerQuery 25 (&aRowIds) to aRows

The native expression is returned as one of the query's paFields columns. See the cDbQuery reference and Bind_Native_Expression for the full query API.

On the control side, OnSetCalculatedValue (on cBaseDEO_Mixin) lets a data-entry object adjust a calculated display value before it is used.

Where this is heading: back-end-specific data binding is expanding toward binding calculated values through native expressions more broadly, and toward back-end-specific filtering at the constraint level. In the client/server WebApp model the intent is for business rules to be validated on the client and always revalidated on the server. These are planned directions; today, native-expression query columns and the calculated-value hook above are the supported pieces.

Checklist¶

1. Find the Object ... is a c...DataDictionary that owns the field's table.
2. Make sure the view, group, list, or column container uses the correct Set Server or Set Main_DD for the binding context.
3. Replace Entry_Item Table.Field with Entry_Item DataDictionaryObject.Field.
4. Keep the field name after the dot unchanged unless the field itself was renamed.
5. For related fields, bind through the related DD object and connect the relationship with Set DDO_Server.