Add gui for setting/exposing constraints in field properties

Provider set constraints cannot be changed by users, ie
if a not null constraint is set on the field at the database
then QGIS users cannot clear this constraint.

src/app/qgsattributetypedialog.cpp

@@ -176,6 +176,23 @@ bool QgsAttributeTypeDialog::fieldEditable() const
   return isFieldEditableCheckBox->isChecked();
 }
 
+void QgsAttributeTypeDialog::setProviderConstraints( QgsVectorDataProvider::Constraints constraints )
+{
+  if ( constraints & QgsVectorDataProvider::ConstraintNotNull )
+  {
+    notNullCheckBox->setChecked( true );
+    notNullCheckBox->setEnabled( false );
+    notNullCheckBox->setToolTip( tr( "The provider for this layer has a NOT NULL constraint set on the field." ) );
+  }
+
+  if ( constraints & QgsVectorDataProvider::ConstraintUnique )
+  {
+    mUniqueCheckBox->setChecked( true );
+    mUniqueCheckBox->setEnabled( false );
+    mUniqueCheckBox->setToolTip( tr( "The provider for this layer has a UNIQUE constraint set on the field." ) );
+  }
+}
+
 void QgsAttributeTypeDialog::setNotNull( bool notNull )
 {
   notNullCheckBox->setChecked( notNull );
@@ -201,6 +218,16 @@ bool QgsAttributeTypeDialog::notNull() const
   return notNullCheckBox->isChecked();
 }
 
+void QgsAttributeTypeDialog::setUnique( bool unique )
+{
+  mUniqueCheckBox->setChecked( unique );
+}
+
+bool QgsAttributeTypeDialog::unique() const
+{
+  return mUniqueCheckBox->isChecked();
+}
+
 void QgsAttributeTypeDialog::setConstraintExpression( const QString &str )
 {
   constraintExpressionWidget->setField( str );

src/app/qgsattributetypedialog.h

@@ -21,6 +21,7 @@
 
 #include "qgseditorconfigwidget.h"
 #include "qgsfeature.h"
+#include "qgsvectordataprovider.h"
 
 class QDialog;
 
@@ -69,6 +70,11 @@ class APP_EXPORT QgsAttributeTypeDialog: public QDialog, private Ui::QgsAttribut
      */
     bool fieldEditable() const;
 
+    /**
+     * Sets any provider side constraints which may affect this field's behaviour.
+     */
+    void setProviderConstraints( QgsVectorDataProvider::Constraints constraints );
+
     /**
      * Setter for checkbox for not null
      */
@@ -79,6 +85,16 @@ class APP_EXPORT QgsAttributeTypeDialog: public QDialog, private Ui::QgsAttribut
      */
     bool notNull() const;
 
+    /**
+     * Setter for unique constraint checkbox
+     */
+    void setUnique( bool unique );
+
+    /**
+     * Getter for unique constraint checkbox state
+     */
+    bool unique() const;
+
     /**
      * Setter for constraint expression description
      * @param desc the expression description

src/app/qgsfieldsproperties.cpp

@@ -559,6 +559,12 @@ void QgsFieldsProperties::attributeTypeDialog()
   attributeTypeDialog.setFieldEditable( cfg.mEditable );
   attributeTypeDialog.setLabelOnTop( cfg.mLabelOnTop );
   attributeTypeDialog.setNotNull( cfg.mNotNull );
+
+  if ( mLayer->fields().fieldOrigin( index ) == QgsFields::OriginProvider )
+  {
+    attributeTypeDialog.setProviderConstraints( mLayer->dataProvider()->fieldConstraints( mLayer->fields().fieldOriginIndex( index ) ) );
+  }
+
   attributeTypeDialog.setConstraintExpression( cfg.mConstraint );
   attributeTypeDialog.setConstraintExpressionDescription( cfg.mConstraintDescription );
   attributeTypeDialog.setDefaultValueExpression( mLayer->defaultValueExpression( index ) );

src/ui/qgsattributetypeedit.ui

@@ -30,6 +30,13 @@
         </property>
        </widget>
       </item>
+      <item>
+       <widget class="QCheckBox" name="mUniqueCheckBox">
+        <property name="text">
+         <string>Unique</string>
+        </property>
+       </widget>
+      </item>
       <item>
        <layout class="QHBoxLayout" name="horizontalLayout_2">
         <property name="topMargin">
@@ -144,18 +151,18 @@
   </layout>
  </widget>
  <customwidgets>
-  <customwidget>
-   <class>QgsExpressionLineEdit</class>
-   <extends>QWidget</extends>
-   <header>qgsexpressionlineedit.h</header>
-   <container>1</container>
-  </customwidget>
   <customwidget>
    <class>QgsCollapsibleGroupBox</class>
    <extends>QGroupBox</extends>
    <header>qgscollapsiblegroupbox.h</header>
    <container>1</container>
   </customwidget>
+  <customwidget>
+   <class>QgsExpressionLineEdit</class>
+   <extends>QWidget</extends>
+   <header>qgsexpressionlineedit.h</header>
+   <container>1</container>
+  </customwidget>
   <customwidget>
    <class>QgsFieldExpressionWidget</class>
    <extends>QWidget</extends>
@@ -169,6 +176,7 @@
   <tabstop>labelOnTopCheckBox</tabstop>
   <tabstop>mExpressionWidget</tabstop>
   <tabstop>notNullCheckBox</tabstop>
+  <tabstop>mUniqueCheckBox</tabstop>
   <tabstop>constraintExpressionWidget</tabstop>
   <tabstop>leConstraintExpressionDescription</tabstop>
  </tabstops>