Support Optionals in Case Expressions

Author: jeffgbutler

CHANGELOG.md

@@ -6,6 +6,8 @@ This log will detail notable changes to MyBatis Dynamic SQL. Full details are av
 
 This is a minor release with several enhancements.
 
+**Important:** This is the last release that will be compatible with Java 8.
+
 GitHub milestone: [https://github.com/mybatis/mybatis-dynamic-sql/milestone/13?closed=1](https://github.com/mybatis/mybatis-dynamic-sql/milestone/13?closed=1)
 
 ### Case Expressions and Cast Function

src/main/java/org/mybatis/dynamic/sql/select/render/SimpleCaseWhenConditionRenderer.java

@@ -46,9 +46,14 @@ public SimpleCaseWhenConditionRenderer(RenderingContext renderingContext, Bindab
 
     @Override
     public FragmentAndParameters visit(ConditionBasedWhenCondition<T> whenCondition) {
-        return whenCondition.conditions().map(this::renderCondition)
-                .collect(FragmentCollector.collect())
-                .toFragmentAndParameters(Collectors.joining(", ")); //$NON-NLS-1$
+        FragmentCollector fragmentCollector = whenCondition.conditions()
+                .filter(this::shouldRender)
+                .map(this::renderCondition)
+                .collect(FragmentCollector.collect());
+
+        Validator.assertFalse(fragmentCollector.isEmpty(), "ERROR.39"); //$NON-NLS-1$
+
+        return fragmentCollector.toFragmentAndParameters(Collectors.joining(", ")); //$NON-NLS-1$
     }
 
     @Override
@@ -58,8 +63,11 @@ public FragmentAndParameters visit(BasicWhenCondition<T> whenCondition) {
                 .toFragmentAndParameters(Collectors.joining(", ")); //$NON-NLS-1$
     }
 
+    private boolean shouldRender(VisitableCondition<T> condition) {
+        return condition.shouldRender(renderingContext);
+    }
+
     private FragmentAndParameters renderCondition(VisitableCondition<T> condition) {
-        Validator.assertTrue(condition.shouldRender(renderingContext), "ERROR.39"); //$NON-NLS-1$
         return condition.accept(conditionVisitor);
     }
 

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

@@ -66,6 +66,10 @@ public boolean hasMultipleFragments() {
         return fragments.size() > 1;
     }
 
+    public boolean isEmpty() {
+        return fragments.isEmpty();
+    }
+
     public static Collector<FragmentAndParameters, FragmentCollector, FragmentCollector> collect() {
         return Collector.of(FragmentCollector::new,
                 FragmentCollector::add,

src/main/resources/org/mybatis/dynamic/sql/util/messages.properties

@@ -55,7 +55,7 @@ ERROR.35=Multi-select statements must have at least one "union" or "union all" e
 ERROR.36=You must either implement the "render" or  "renderWithTableAlias" method in a column or function
 ERROR.37=The "{0}" function does not support conditions that fail to render
 ERROR.38=Bound values cannot be aliased
-ERROR.39=When clauses in case expressions must render (optional conditions are not supported)
+ERROR.39=When clauses in case expressions must render
 ERROR.40=Case expressions must have at least one "when" clause
 ERROR.41=You cannot call "then" in a Kotlin case expression more than once
 ERROR.42=You cannot call `else` in a Kotlin case expression more than once

src/site/markdown/docs/caseExpressions.md

@@ -180,8 +180,8 @@ select(case_()
 ```
 
 The full syntax of "where" and "having" clauses is supported in the "when" clause - but that may or may not be supported
-by your database. Testing is crucial. In addition, the library does not support conditions that don't render in a case
-statement - so avoid the use of conditions like "isEqualToWhenPresent", etc.
+by your database. Testing is crucial. The library supports optional conditions in "when" clauses, but at least one
+condition must render, else the library will throw an `InvalidSqlException`.
 
 The rendered SQL will be as follows (without the line breaks):
 ```sql

src/site/markdown/docs/kotlinCaseExpressions.md

@@ -200,8 +200,8 @@ select(case {
 ```
 
 The full syntax of "where" and "having" clauses is supported in the "when" clause - but that may or may not be supported
-by your database. Testing is crucial. In addition, the library does not support conditions that don't render in a case
-statement - so avoid the use of conditions like "isEqualToWhenPresent", etc.
+by your database. Testing is crucial. The library supports optional conditions in "when" clauses, but at least one
+condition must render, else the library will throw an `InvalidSqlException`.
 
 The rendered SQL will be as follows (without the line breaks):
 ```sql