Export child table

What do you mean by "exporting records to a child table"? 

- Copy records to the same database?

- Copy records to another database? 

Do you mean you want to export a child table from the parent?

You can always just go to the actual table and export the data.

You have several solutions:

1 : Automatically open the table you want to export using ui.openTable 

var tableName := "Invoice";
var tabName := "All Invoices";
var fileName := "myExport2.csv";
var exportSettings := {
    sep: ",",
    qut: """",
    lf: "%0D%0A",
    numberFormat: "point",
    dateFormat: "locale",
    header: true,
    sepHeader: false,
    encoding: "utf8"
}
var data := #{:text:callback
    //save current view display
    var ns = ui.currentView.getNavigationState();
    // retrieve type Id from tableName
    var tid = database.schema.findType(tableName) && database.schema.findType(tableName).id;
    // retrieve view from type Id and tab Id
    var view = tid && Object.values(database.views).find(v => { return v.type == tid && v.caption == tabName })
    //Open table with specifique tab
    if (view) {
        ui.openTable(tid, view.id);
        window.util.renderCSV(window.database, window.ui.currentView.table, exportSettings)
            .then((textData) => {
                callback(textData);
            })
    }
    else
        callback(`view ${tableName}:${tabName} not found !`)
    //re open previous view
    ui.openTable(ns.tid, ns.vid);
}#;
createTextFile( this, data, fileName );

2 : Simulate the display of a table and export the object thus constructed

var fileName := "myExport2.csv";
var tableName := "Customer";
var tabName := "All customers";
var exportSettings := {
    sep: ",",
    qut: """",
    lf: "%0D%0A",
    numberFormat: "point",
    dateFormat: "locale",
    header: true,
    sepHeader: false,
    encoding: "utf8"
}
var data := #{:text:callback
    debugger;
    // duplicate table object from ui.views.table.table
    var table = Object.assign({}, ui.views.table.table, Object.getPrototypeOf(ui.views.table.table))
//    var table = Object.assign({}, ui.currentView.table, Object.getPrototypeOf(ui.currentView.table))
    // clear display function
    table.createCells = () => { };
    table.updateRows = () => {};
    table.updateHead = () => {};
    table.updateFoot = () => {};
    table.retainSelection = () => {};
    // retrieve type Id from tableName
    var tid = database.schema.findType(tableName) && database.schema.findType(tableName).id;
    // retrieve view from type Id and tab Id
    var view = tid && Object.values(database.views).find(v => { return v.type == tid && v.caption == tabName })
    if (view) {
        // initialize the table
        table.setConfig(view.config, {});
        // load the rows
        table.load(() => {
            //render CSV;
            util.renderCSV(database, table, exportSettings)
                .then((textData) => {
                    callback(textData);
                })
        })
    }
    else
        callback(`view ${tableName}:${tabName} not found !`)
}#;
createTextFile( this, data, fileName );

3 : Build the string yourself by compiling all the fields you want to appear in your file. This may be the simplest solution in the end, right?