Add a field on the fly by using the AddFieldFromExpression method.
Information noteThe expression of a field on the fly is persisted but not its values.
Example
1. Add the field Lengths in the app.
The client sends:
{
"jsonrpc": "2.0",
"id": 1,
"method": "AddFieldFromExpression",
"handle": 1,
"params": [
"Lengths",
"=len(Country)"
]
}
The engine returns:
{
"jsonrpc": "2.0",
"id": 1,
"result": {
"qSuccess": true
},
"change": [
1
]
}
The field is successfully added to the app.
2. Create a list object in the app. The dimension of the list object is the field Lengths (set in qFieldDefs) that has been added on the fly.
The client sends:
{
"jsonrpc": "2.0",
"id": 2,
"method": "CreateSessionObject",
"handle": 1,
"params": [
{
"qInfo": {
"qId": "",
"qType": "ListObject"
},
"qListObjectDef": {
"qStateName": "$",
"qLibraryId": "",
"qDef": {
"qFieldDefs": [
"Lengths"
],
"qFieldLabels": [
"Label"
],
"qSortCriterias": [
{
"qSortByLoadOrder": 1
}
]
},
"qInitialDataFetch": [
{
"qTop": 0,
"qHeight": 1,
"qLeft": 0,
"qWidth": 1
}
]
}
}
]
}
The engine returns:
{
"jsonrpc": "2.0",
"id": 2,
"result": {
"qReturn": {
"qType": "GenericObject",
"qHandle": 2
}
},
"change": [
2
]
}
The list object is created and has 2 as a handle.
3. Get the first three values of the list object (qHeight is 3 and qTop is 0).
The client sends:
{
"jsonrpc": "2.0",
"id": 3,
"method": "GetListObjectData",
"handle": 2,
"params": [
"/qListObjectDef",
[
{
"qTop": 0,
"qLeft": 0,
"qHeight": 3,
"qWidth": 1
}
]
]
}
The engine returns:
{
"jsonrpc": "2.0",
"id": 3,
"result": {
"qDataPages": [
{
"qMatrix": [
[
{
"qText": "13",
"qNum": 13,
"qElemNumber": 0,
"qState": "O"
}
],
[
{
"qText": "14",
"qNum": 14,
"qElemNumber": 1,
"qState": "O"
}
],
[
{
"qText": "8",
"qNum": 8,
"qElemNumber": 2,
"qState": "O"
}
]
],
"qTails": [],
"qArea": {
"qLeft": 0,
"qTop": 0,
"qWidth": 1,
"qHeight": 3
}
}
]
}
}
The first three values are returned. They give the length of the field Country.