From a91d5043994f92f64b77f70ab21a56bacc2ab675 Mon Sep 17 00:00:00 2001
From: knoobie <knoobie@gmx.de>
Date: Wed, 24 Mar 2021 10:52:53 +0100
Subject: [PATCH] fix: Add API to control whether Binder converts back to
 presentation (CP: #10343)

---
 .../com/vaadin/flow/data/binder/Binder.java   | 58 ++++++++++++++++++-
 .../vaadin/flow/data/binder/BinderTest.java   | 17 +++++-
 2 files changed, 73 insertions(+), 2 deletions(-)

diff --git a/flow-data/src/main/java/com/vaadin/flow/data/binder/Binder.java b/flow-data/src/main/java/com/vaadin/flow/data/binder/Binder.java
index 225fa7197fb..f41950b5f8d 100644
--- a/flow-data/src/main/java/com/vaadin/flow/data/binder/Binder.java
+++ b/flow-data/src/main/java/com/vaadin/flow/data/binder/Binder.java
@@ -250,6 +250,32 @@ default BindingValidationStatus<TARGET> validate() {
          * @return A boolean value.
          */
         public boolean isValidatorsDisabled();
+
+        /**
+         * Define whether the value should be converted back to the presentation
+         * in the field when a converter is used in binding.
+         * <p>
+         * As of version 6.0, when a converter is used on a binding and the user
+         * input value is modified by the converter, the value from the converter
+         * is applied back to the input. It is possible to control this behavior
+         * with this API.
+         *
+         * @see BindingBuilder#withConverter(Converter)
+         * @see BindingBuilder#withConverter(SerializableFunction, SerializableFunction)
+         * @see BindingBuilder#withConverter(SerializableFunction, SerializableFunction, String)
+         *
+         * @param convertBackToPresentation
+         *            A boolean value
+         */
+        void setConvertBackToPresentation(boolean convertBackToPresentation);
+
+        /**
+         * Returns whether the value is converted back to the presentation in
+         * the field when a converter is used in binding.
+         *
+         * @return A boolean value
+         */
+        boolean isConvertBackToPresentation();
     }
 
     /**
@@ -508,6 +534,12 @@ default BindingBuilder<BEAN, TARGET> withValidator(
          * For instance, a {@code TextField} can be bound to an integer-typed
          * property using an appropriate converter such as a
          * {@link StringToIntegerConverter}.
+         * <p>
+         * The converted value is applied back to the field by default,
+         * this can be controlled with the method
+         * {@link Binding#setConvertBackToPresentation(boolean)}.
+         *
+         * @see Binding#setConvertBackToPresentation(boolean)
          *
          * @param <NEWTARGET>
          *            the type to convert to
@@ -534,6 +566,12 @@ <NEWTARGET> BindingBuilder<BEAN, NEWTARGET> withConverter(
          * For instance, a {@code TextField} can be bound to an integer-typed
          * property using appropriate functions such as:
          * <code>withConverter(Integer::valueOf, String::valueOf);</code>
+         * <p>
+         * The converted value is applied back to the field by default,
+         * this can be controlled with the method
+         * {@link Binding#setConvertBackToPresentation(boolean)}.
+         *
+         * @see Binding#setConvertBackToPresentation(boolean)
          *
          * @param <NEWTARGET>
          *            the type to convert to
@@ -569,6 +607,12 @@ default <NEWTARGET> BindingBuilder<BEAN, NEWTARGET> withConverter(
          * For instance, a {@code TextField} can be bound to an integer-typed
          * property using appropriate functions such as:
          * <code>withConverter(Integer::valueOf, String::valueOf);</code>
+         * <p>
+         * The converted value is applied back to the field by default,
+         * this can be controlled with the method
+         * {@link Binding#setConvertBackToPresentation(boolean)}.
+         *
+         * @see Binding#setConvertBackToPresentation(boolean)
          *
          * @param <NEWTARGET>
          *            the type to convert to
@@ -1055,6 +1099,8 @@ protected static class BindingImpl<BEAN, FIELDVALUE, TARGET>
 
         private boolean validatorsDisabled = false;
 
+        private boolean convertBackToPresentation = true;
+
         public BindingImpl(BindingBuilderImpl<BEAN, FIELDVALUE, TARGET> builder,
                 ValueProvider<BEAN, TARGET> getter,
                 Setter<BEAN, TARGET> setter) {
@@ -1246,7 +1292,7 @@ private BindingValidationStatus<TARGET> writeFieldValue(BEAN bean) {
             if (!isReadOnly()) {
                 result.ifOk(value -> {
                     setter.accept(bean, value);
-                    if (value != null) {
+                    if (convertBackToPresentation && value != null) {
                         FIELDVALUE converted = convertToFieldType(value);
                         if (!field.getValue().equals(converted)) {
                             getField().setValue(converted);
@@ -1353,6 +1399,16 @@ public void setValidatorsDisabled(boolean validatorsDisabled) {
         public boolean isValidatorsDisabled() {
             return validatorsDisabled;
         }
+
+        @Override
+        public void setConvertBackToPresentation(boolean convertBackToPresentation) {
+            this.convertBackToPresentation = convertBackToPresentation;
+        }
+
+        @Override
+        public boolean isConvertBackToPresentation() {
+            return convertBackToPresentation;
+        }
     }
 
     /**
diff --git a/flow-data/src/test/java/com/vaadin/flow/data/binder/BinderTest.java b/flow-data/src/test/java/com/vaadin/flow/data/binder/BinderTest.java
index 357724bf70e..73a3a60c92b 100644
--- a/flow-data/src/test/java/com/vaadin/flow/data/binder/BinderTest.java
+++ b/flow-data/src/test/java/com/vaadin/flow/data/binder/BinderTest.java
@@ -583,7 +583,22 @@ public void withConverter_writeBackValue() {
         // € 10.00
         assertEquals("€ " + new DecimalFormat("0.00").format(10),
                 rentField.getValue());
-    } 
+    }
+
+    @Test
+    public void withConverter_writeBackValueDisabled() {
+        TestTextField rentField = new TestTextField();
+        rentField.setValue("");
+        Binding<Person, BigDecimal> binding = binder.forField(rentField)
+          .withConverter(new EuroConverter(""))
+          .withNullRepresentation(BigDecimal.valueOf(0d))
+          .bind(Person::getRent, Person::setRent);
+        binder.setBean(item);
+        binding.setConvertBackToPresentation(false);
+        rentField.setValue("10");
+
+        assertNotEquals("€ 10.00", rentField.getValue());
+    }
 
     @Test
     public void beanBinder_nullRepresentationIsNotDisabled() {