TableModel: add roleDataProvider callback

As an alternative to trying to write smarter C++ in the data() accessor, we
give the user full control of data conversion by calling an external JS
function if defined, to map role to the value that data() should return.
This enables extracting arbitrary values, converting the data in arbitrary
ways, or even doing calculations in case the EditRole stores a formula and the
DisplayRole should provide the result, or something like that.

This callback is implemented somewhat like TableView.columnWidthProvider, but
the arguments are more complex: function(row, column, role, rawData)

Change-Id: Ifaf5807f4809e0b5ad1d1c403f65c0707b902f10
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

3 files changed, 129 insertions, 0 deletions

diff --git a/src/qml/doc/snippets/qml/tablemodel/roleDataProvider.qml b/src/qml/doc/snippets/qml/tablemodel/roleDataProvider.qml
new file mode 100644
index 0000000000..6c8ae3f1fc
--- /dev/null
+++ b/src/qml/doc/snippets/qml/tablemodel/roleDataProvider.qml
@@ -0,0 +1,83 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+import QtQuick 2.12
+import Qt.labs.qmlmodels 1.0
+
+TableView {
+    columnSpacing: 1; rowSpacing: 1
+    model:  TableModel {
+        property real taxPercent: 10
+        rows: [
+            [{ fruitType: "Apple" }, { fruitPrice: 1.50 }],
+            [{ fruitType: "Orange" }, { fruitPrice: 2.50 }]
+        ]
+        roleDataProvider: function(row, column, role, cellData) {
+            if (role === "display") {
+                if (cellData.hasOwnProperty("fruitPrice")) {
+                    console.log("taxing your fruit " + JSON.stringify(cellData))
+                    return (cellData.fruitPrice * (1 + taxPercent / 100)).toFixed(2);
+                }
+                else if (cellData.hasOwnProperty("fruitType"))
+                    return cellData.fruitType;
+            }
+            return cellData;
+        }
+    }
+    delegate: Rectangle {
+        implicitWidth: 150; implicitHeight: 30
+        color: "lightsteelblue"
+        Text {
+            x: 6; anchors.verticalCenter: parent.verticalCenter
+            text: display
+        }
+    }
+}
+//![0]
diff --git a/src/qml/types/qqmltablemodel.cpp b/src/qml/types/qqmltablemodel.cpp
index cf3fc0298a..9bf8c7f562 100644
--- a/src/qml/types/qqmltablemodel.cpp
+++ b/src/qml/types/qqmltablemodel.cpp
@@ -548,6 +548,38 @@ void QQmlTableModel::setRow(int rowIndex, const QVariant &row)
     }
 }
 
+/*!
+    \qmlproperty var TableModel::roleDataProvider
+
+    This property can hold a function that will map roles to values.
+
+    When assigned, it will be called each time data() is called, to enable
+    extracting arbitrary values, converting the data in arbitrary ways, or even
+    doing calculations. It takes 4 arguments: \c row, \c column, \c role (as a
+    string), and \c cellData, which is the complete data that is stored in the
+    given cell. (If the cell contains a JS object with multiple named values,
+    the entire object will be given in cellData.) The function that you define
+    must return the value to be used; for example a typical delegate will
+    display the value returned for the \c display role, so you can check
+    whether that is the role and return data in a form that is suitable for the
+    delegate to show:
+
+    \snippet qml/tablemodel/roleDataProvider.qml 0
+*/
+QJSValue QQmlTableModel::roleDataProvider() const
+{
+    return mRoleDataProvider;
+}
+
+void QQmlTableModel::setRoleDataProvider(QJSValue roleDataProvider)
+{
+    if (roleDataProvider.strictlyEquals(mRoleDataProvider))
+        return;
+
+    mRoleDataProvider = roleDataProvider;
+    emit roleDataProviderChanged();
+}
+
 QModelIndex QQmlTableModel::index(int row, int column, const QModelIndex &parent) const
 {
     return row >= 0 && row < rowCount() && column >= 0 && column < columnCount() && !parent.isValid()
@@ -603,6 +635,14 @@ QVariant QQmlTableModel::data(const QModelIndex &index, int role) const
         return QVariant();
 
     const QVariantList rowData = mRows.at(row).toList();
+
+    if (mRoleDataProvider.isCallable()) {
+        const auto args = QJSValueList() << row << column <<
+                                            QString::fromUtf8(mRoleNames.value(role)) <<
+                                            qmlEngine(this)->toScriptValue(rowData.at(column));
+        return const_cast<QQmlTableModel*>(this)->mRoleDataProvider.call(args).toVariant();
+    }
+
     const QVariantMap columnData = rowData.at(column).toMap();
 
     int effectiveRole = role;
diff --git a/src/qml/types/qqmltablemodel_p.h b/src/qml/types/qqmltablemodel_p.h
index 8da930872d..863c592678 100644
--- a/src/qml/types/qqmltablemodel_p.h
+++ b/src/qml/types/qqmltablemodel_p.h
@@ -65,6 +65,7 @@ class Q_QML_PRIVATE_EXPORT QQmlTableModel : public QAbstractTableModel
     Q_PROPERTY(int columnCount READ columnCount NOTIFY columnCountChanged FINAL)
     Q_PROPERTY(int rowCount READ rowCount NOTIFY rowCountChanged FINAL)
     Q_PROPERTY(QVariant rows READ rows WRITE setRows NOTIFY rowsChanged FINAL)
+    Q_PROPERTY(QJSValue roleDataProvider READ roleDataProvider WRITE setRoleDataProvider NOTIFY roleDataProviderChanged)
 
 public:
     QQmlTableModel(QObject *parent = nullptr);
@@ -81,6 +82,9 @@ public:
     Q_INVOKABLE void removeRow(int rowIndex, int rows = 1);
     Q_INVOKABLE void setRow(int rowIndex, const QVariant &row);
 
+    QJSValue roleDataProvider() const;
+    void setRoleDataProvider(QJSValue roleDataProvider);
+
     QModelIndex index(int row, int column, const QModelIndex &parent) const override;
     int rowCount(const QModelIndex &parent = QModelIndex()) const override;
     int columnCount(const QModelIndex &parent = QModelIndex()) const override;
@@ -92,6 +96,7 @@ Q_SIGNALS:
     void columnCountChanged();
     void rowCountChanged();
     void rowsChanged();
+    void roleDataProviderChanged();
 
 private:
     class ColumnPropertyInfo
@@ -136,6 +141,7 @@ private:
     // key = column index
     // value = index (key) into mRoleNames
     QHash<int, int> mDefaultDisplayRoles;
+    QJSValue mRoleDataProvider;
 };
 
 QT_END_NAMESPACE