Allow usage of Conditions in SELECT projections

pom.xml

@@ -5,7 +5,7 @@
 
 	<groupId>org.springframework.data</groupId>
 	<artifactId>spring-data-relational-parent</artifactId>
-	<version>2.3.0-SNAPSHOT</version>
+	<version>2.3.0-1007-selectbuild-accept-conditions-SNAPSHOT</version>
 	<packaging>pom</packaging>
 
 	<name>Spring Data Relational Parent</name>

spring-data-jdbc-distribution/pom.xml

@@ -14,7 +14,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-relational-parent</artifactId>
-		<version>2.3.0-SNAPSHOT</version>
+		<version>2.3.0-1007-selectbuild-accept-conditions-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-jdbc/pom.xml

@@ -6,7 +6,7 @@
 	<modelVersion>4.0.0</modelVersion>
 
 	<artifactId>spring-data-jdbc</artifactId>
-	<version>2.3.0-SNAPSHOT</version>
+	<version>2.3.0-1007-selectbuild-accept-conditions-SNAPSHOT</version>
 
 	<name>Spring Data JDBC</name>
 	<description>Spring Data module for JDBC repositories.</description>
@@ -15,7 +15,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-relational-parent</artifactId>
-		<version>2.3.0-SNAPSHOT</version>
+		<version>2.3.0-1007-selectbuild-accept-conditions-SNAPSHOT</version>
 	</parent>
 
 	<properties>

spring-data-relational/pom.xml

@@ -6,15 +6,15 @@
 	<modelVersion>4.0.0</modelVersion>
 
 	<artifactId>spring-data-relational</artifactId>
-	<version>2.3.0-SNAPSHOT</version>
+	<version>2.3.0-1007-selectbuild-accept-conditions-SNAPSHOT</version>
 
 	<name>Spring Data Relational</name>
 	<description>Spring Data Relational support</description>
 
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-relational-parent</artifactId>
-		<version>2.3.0-SNAPSHOT</version>
+		<version>2.3.0-1007-selectbuild-accept-conditions-SNAPSHOT</version>
 	</parent>
 
 	<properties>

spring-data-relational/src/main/java/org/springframework/data/relational/core/sql/Condition.java

@@ -23,7 +23,7 @@
  * @since 1.1
  * @see Conditions
  */
-public interface Condition extends Segment {
+public interface Condition extends Segment, Expression {
 
 	/**
 	 * Combine another {@link Condition} using {@code AND}.

spring-data-relational/src/main/java/org/springframework/data/relational/core/sql/render/ComparisonVisitor.java

@@ -52,14 +52,14 @@ class ComparisonVisitor extends FilteredSubtreeVisitor {
 	@Override
 	Delegation enterNested(Visitable segment) {
 
-		if (segment instanceof Expression) {
-			ExpressionVisitor visitor = new ExpressionVisitor(context);
+		if (segment instanceof Condition) {
+			ConditionVisitor visitor = new ConditionVisitor(context);
 			current = visitor;
 			return Delegation.delegateTo(visitor);
 		}
 
-		if (segment instanceof Condition) {
-			ConditionVisitor visitor = new ConditionVisitor(context);
+		if (segment instanceof Expression) {
+			ExpressionVisitor visitor = new ExpressionVisitor(context);
 			current = visitor;
 			return Delegation.delegateTo(visitor);
 		}

spring-data-relational/src/main/java/org/springframework/data/relational/core/sql/render/FilteredSingleConditionRenderSupport.java

@@ -28,6 +28,7 @@
  * and delegate nested {@link Expression} and {@link Condition} rendering.
  *
  * @author Mark Paluch
+ * @author Jens Schauder
  * @since 1.1
  */
 abstract class FilteredSingleConditionRenderSupport extends FilteredSubtreeVisitor {
@@ -55,18 +56,19 @@ abstract class FilteredSingleConditionRenderSupport extends FilteredSubtreeVisit
 	@Override
 	Delegation enterNested(Visitable segment) {
 
-		if (segment instanceof Expression) {
-			ExpressionVisitor visitor = new ExpressionVisitor(context);
+		if (segment instanceof Condition) {
+			ConditionVisitor visitor = new ConditionVisitor(context);
 			current = visitor;
 			return Delegation.delegateTo(visitor);
 		}
 
-		if (segment instanceof Condition) {
-			ConditionVisitor visitor = new ConditionVisitor(context);
+		if (segment instanceof Expression) {
+			ExpressionVisitor visitor = new ExpressionVisitor(context);
 			current = visitor;
 			return Delegation.delegateTo(visitor);
 		}
 
+
 		throw new IllegalStateException("Cannot provide visitor for " + segment);
 	}
 

spring-data-relational/src/test/java/org/springframework/data/relational/core/sql/render/SelectRendererUnitTests.java

@@ -467,4 +467,18 @@ void shouldRenderCast() {
 		final String rendered = SqlRenderer.toString(select);
 		assertThat(rendered).isEqualTo("SELECT CAST(User.name AS VARCHAR2) FROM User");
 	}
+
+	@Test // GH-1007
+	void shouldRenderConditionAsExpression() {
+
+		Table table = SQL.table("User");
+		Select select = StatementBuilder.select( //
+				Conditions.isGreater(table.column("age"), SQL.literalOf(18)) //
+		) //
+				.from(table) //
+				.build();
+
+		final String rendered = SqlRenderer.toString(select);
+		assertThat(rendered).isEqualTo("SELECT User.age > 18 FROM User");
+	}
 }