Parameter type converter can be compatible with Spring converters

Author: jeffgbutler

src/main/java/org/mybatis/dynamic/sql/BindableColumn.java

@@ -47,8 +47,8 @@ default Optional<String> typeHandler() {
     default Optional<RenderingStrategy> renderingStrategy() {
         return Optional.empty();
     }
-
-    default Optional<ParameterTypeConverter<T>> parameterTypeConverter() {
-        return Optional.empty();
+    
+    default Object convertParameterType(T value) {
+        return value;
     }
 }

src/main/java/org/mybatis/dynamic/sql/ParameterTypeConverter.java

@@ -17,7 +17,7 @@
 
 /**
  * A parameter type converter is used to change a parameter value from one type to another
- * during statement rendering before the parameter is placed into the parameter map. This can be used
+ * during statement rendering and before the parameter is placed into the parameter map. This can be used
  * to somewhat mimic the function of a MyBatis type handler for runtimes such as Spring that don't have
  * a corresponding concept.
  * 
@@ -28,27 +28,27 @@
  *
  * <p>A parameter type converter is associated with a SqlColumn.
  * 
- * <p>A parameter type converter is compatible with Spring's general Converter interface so existing converters
- * can be reused here if they are marked with this additional interface. The return type is always Object as the
- * converter is called immediately before a value is placed into a parameter Map and there is no longer any need for
- * the actual target type. Having a fixed return type removes quite a few generic hurdles.
+ * <p>This interface is based on Spring's general Converter interface and is intentionally compatible with it.
+ * Existing converters may be reused if they are marked with this additional interface.
  *
- * <p>The converter is only used for parameters - it is not used for result set processing. The converter will be
- * called in the following circumstances:
+ * <p>The converter is only used for parameters in a parameter map. It is not used for result set processing.
+ * It is also not used for insert statements that are based on an external record class. The converter will be called
+ * in the following circumstances:
  *
  * <ul>
- *     <li>Parameters in a general insert statement</li>
- *     <li>Parameters in an update statement</li>
- *     <li>Parameters in a where clause in any statement</li>
+ *     <li>Parameters in a general insert statement (for the Value and ValueWhenPresent mappings)</li>
+ *     <li>Parameters in an update statement (for the Value and ValueWhenPresent mappings)</li>
+ *     <li>Parameters in a where clause in any statement (for conditions that accept a value or multiple values)</li>
  * </ul>
  * 
  * @param <S> Source Type
+ * @param <T> Target Type
  *
  * @see SqlColumn
  * @author Jeff Butler
  * @since 1.1.5
  */
 @FunctionalInterface
-public interface ParameterTypeConverter<S> {
-    Object convert(S source);
+public interface ParameterTypeConverter<S, T> {
+    T convert(S source);
 }

src/main/java/org/mybatis/dynamic/sql/SqlColumn.java

@@ -31,7 +31,7 @@ public class SqlColumn<T> implements BindableColumn<T>, SortSpecification {
     protected String alias;
     protected String typeHandler;
     protected RenderingStrategy renderingStrategy;
-    protected ParameterTypeConverter<T> parameterTypeConverter;
+    protected ParameterTypeConverter<T, ?> parameterTypeConverter;
 
     private SqlColumn(Builder builder) {
         name = Objects.requireNonNull(builder.name);
@@ -49,7 +49,7 @@ protected SqlColumn(SqlColumn<?> sqlColumn) {
         alias = sqlColumn.alias;
         typeHandler = sqlColumn.typeHandler;
         renderingStrategy = sqlColumn.renderingStrategy;
-        parameterTypeConverter = (ParameterTypeConverter<T>) sqlColumn.parameterTypeConverter;
+        parameterTypeConverter = (ParameterTypeConverter<T, ?>) sqlColumn.parameterTypeConverter;
     }
 
     public String name() {
@@ -76,8 +76,8 @@ public Optional<String> typeHandler() {
     }
 
     @Override
-    public Optional<ParameterTypeConverter<T>> parameterTypeConverter() {
-        return Optional.ofNullable(parameterTypeConverter);
+    public Object convertParameterType(T value) {
+        return parameterTypeConverter == null ? value : parameterTypeConverter.convert(value);
     }
 
     @Override
@@ -128,7 +128,7 @@ public <S> SqlColumn<S> withRenderingStrategy(RenderingStrategy renderingStrateg
         return column;
     }
 
-    public <S> SqlColumn<S> withParameterTypeConverter(ParameterTypeConverter<S> parameterTypeConverter) {
+    public <S> SqlColumn<S> withParameterTypeConverter(ParameterTypeConverter<S, ?> parameterTypeConverter) {
         SqlColumn<S> column = new SqlColumn<>(this);
         column.parameterTypeConverter = parameterTypeConverter;
         return column;

src/main/java/org/mybatis/dynamic/sql/util/ValueMapping.java

@@ -33,8 +33,7 @@ private ValueMapping(SqlColumn<T> column, Supplier<T> valueSupplier) {
     }
 
     public Object value() {
-        return localColumn.parameterTypeConverter().map(tc -> tc.convert(valueSupplier.get()))
-                .orElseGet(valueSupplier);
+        return localColumn.convertParameterType(valueSupplier.get());
     }
 
     @Override

src/main/java/org/mybatis/dynamic/sql/util/ValueWhenPresentMapping.java

@@ -38,7 +38,7 @@ public Optional<Object> value() {
     }
 
     private Object convert(T value) {
-        return localColumn.parameterTypeConverter().map(tc -> tc.convert(value)).orElse(value);
+        return localColumn.convertParameterType(value);
     }
 
     @Override

src/main/java/org/mybatis/dynamic/sql/where/render/WhereConditionVisitor.java

@@ -118,9 +118,7 @@ public Optional<FragmentAndParameters> visit(AbstractColumnComparisonCondition<T
     }
 
     private Object convertValue(T value) {
-        return column.parameterTypeConverter()
-                .map(tc -> tc.convert(value))
-                .orElse(value);
+        return column.convertParameterType(value);
     }
 
     private FragmentAndParameters toFragmentAndParameters(T value) {

src/test/java/examples/spring/LastNameParameterConverter.java

@@ -18,7 +18,7 @@
 import org.mybatis.dynamic.sql.ParameterTypeConverter;
 import org.springframework.core.convert.converter.Converter;
 
-public class LastNameParameterConverter implements ParameterTypeConverter<LastName>, Converter<LastName, String> {
+public class LastNameParameterConverter implements ParameterTypeConverter<LastName, String>, Converter<LastName, String> {
     @Override
     public String convert(LastName source) {
         return source == null ? null : source.getName();

src/test/java/examples/spring/YesNoParameterConverter.java

@@ -17,7 +17,7 @@
 
 import org.mybatis.dynamic.sql.ParameterTypeConverter;
 
-public class YesNoParameterConverter implements ParameterTypeConverter<Boolean> {
+public class YesNoParameterConverter implements ParameterTypeConverter<Boolean, String> {
 
     @Override
     public String convert(Boolean source) {