feat: add concat or null operator (#93)

Author: aaron-steinfeld

attribute-projection-functions/src/main/java/org/hypertrace/core/attribute/service/projection/functions/ConcatenateOrNull.java

@@ -0,0 +1,16 @@
+package org.hypertrace.core.attribute.service.projection.functions;
+
+import static java.util.Objects.isNull;
+
+import javax.annotation.Nullable;
+
+public class ConcatenateOrNull {
+
+  @Nullable
+  public static String concatenate(@Nullable String first, @Nullable String second) {
+    if (isNull(first) || isNull(second)) {
+      return null;
+    }
+    return first + second;
+  }
+}

attribute-projection-functions/src/test/java/org/hypertrace/core/attribute/service/projection/functions/ConcatenateOrNullTest.java

@@ -0,0 +1,23 @@
+package org.hypertrace.core.attribute.service.projection.functions;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import org.junit.jupiter.api.Test;
+
+class ConcatenateOrNullTest {
+
+  @Test
+  void concatenatesNormalStrings() {
+    assertEquals("foobar", ConcatenateOrNull.concatenate("foo", "bar"));
+    assertEquals("foo", ConcatenateOrNull.concatenate("foo", ""));
+    assertEquals("bar", ConcatenateOrNull.concatenate("", "bar"));
+  }
+
+  @Test
+  void returnsNullIfAnyNullArgs() {
+    assertNull(ConcatenateOrNull.concatenate("foo", null));
+    assertNull(ConcatenateOrNull.concatenate(null, "bar"));
+    assertNull(ConcatenateOrNull.concatenate(null, null));
+  }
+}

attribute-projection-registry/src/main/java/org/hypertrace/core/attribute/service/projection/AttributeProjectionRegistry.java

@@ -2,19 +2,21 @@
 
 import static org.hypertrace.core.attribute.service.projection.AttributeKindWithNullability.nonNullableKind;
 import static org.hypertrace.core.attribute.service.projection.AttributeKindWithNullability.nullableKind;
-import static org.hypertrace.core.attribute.service.v1.AttributeKind.*;
+import static org.hypertrace.core.attribute.service.v1.AttributeKind.TYPE_BOOL;
+import static org.hypertrace.core.attribute.service.v1.AttributeKind.TYPE_STRING;
 import static org.hypertrace.core.attribute.service.v1.ProjectionOperator.PROJECTION_OPERATOR_CONCAT;
+import static org.hypertrace.core.attribute.service.v1.ProjectionOperator.PROJECTION_OPERATOR_CONCAT_OR_NULL;
 import static org.hypertrace.core.attribute.service.v1.ProjectionOperator.PROJECTION_OPERATOR_CONDITIONAL;
 import static org.hypertrace.core.attribute.service.v1.ProjectionOperator.PROJECTION_OPERATOR_HASH;
 import static org.hypertrace.core.attribute.service.v1.ProjectionOperator.PROJECTION_OPERATOR_STRING_EQUALS;
 
 import java.util.Map;
 import java.util.Optional;
 import org.hypertrace.core.attribute.service.projection.functions.Concatenate;
+import org.hypertrace.core.attribute.service.projection.functions.ConcatenateOrNull;
 import org.hypertrace.core.attribute.service.projection.functions.Conditional;
 import org.hypertrace.core.attribute.service.projection.functions.Equals;
 import org.hypertrace.core.attribute.service.projection.functions.Hash;
-import org.hypertrace.core.attribute.service.v1.AttributeKind;
 import org.hypertrace.core.attribute.service.v1.ProjectionOperator;
 
 public class AttributeProjectionRegistry {
@@ -42,8 +44,13 @@ public class AttributeProjectionRegistry {
               nullableKind(TYPE_BOOL),
               nullableKind(TYPE_STRING),
               nullableKind(TYPE_STRING),
-              Conditional::getValue
-          ));
+              Conditional::getValue),
+          PROJECTION_OPERATOR_CONCAT_OR_NULL,
+          new BinaryAttributeProjection<>(
+              nullableKind(TYPE_STRING),
+              nullableKind(TYPE_STRING),
+              nullableKind(TYPE_STRING),
+              ConcatenateOrNull::concatenate));
 
   public Optional<AttributeProjection> getProjection(ProjectionOperator projectionOperator) {
     return Optional.ofNullable(PROJECTION_MAP.get(projectionOperator));

attribute-service-api/src/main/proto/org/hypertrace/core/attribute/service/v1/attribute_metadata.proto

@@ -187,4 +187,5 @@ enum ProjectionOperator {
   PROJECTION_OPERATOR_HASH = 2;
   PROJECTION_OPERATOR_STRING_EQUALS = 3;
   PROJECTION_OPERATOR_CONDITIONAL = 4;
+  PROJECTION_OPERATOR_CONCAT_OR_NULL = 5;
 }