Coalesce Function (#397)

* Adds coalesce function
ezylang · Sep 21, 2023 · 34846d2 · 34846d2
1 parent 8d59bd2
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diff --git a/docs/references/functions.md b/docs/references/functions.md
@@ -15,6 +15,7 @@ Available through the _ExpressionConfiguration.StandardFunctionsDictionary_ cons
 |--------------------------------------------|-------------------------------------------------------------------------------------------------------------------------|
 | ABS(value)                                 | Absolute (non-negative) value                                                                                           |
 | CEILING(value)                             | Rounds the given value an integer using the rounding mode CEILING                                                       |
+| COALESCE(value, ...)                       | Returns the first non-null parameter, or NULL if all parameters are null                                                |
 | FACT(base)                                 | Calculates the factorial of a base value                                                                                |
 | FLOOR(value)                               | Rounds the given value an integer using the rounding mode FLOOR                                                         |
 | IF(condition, resultIfTrue, resultIfFalse) | Conditional evaluation function. If _condition_ is true, the _resultIfTrue_ is returned, else the _resultIfFalse_ value |

diff --git a/src/main/java/com/ezylang/evalex/config/ExpressionConfiguration.java b/src/main/java/com/ezylang/evalex/config/ExpressionConfiguration.java
@@ -113,6 +113,7 @@ public class ExpressionConfiguration {
           // basic functions
           Map.entry("ABS", new AbsFunction()),
           Map.entry("CEILING", new CeilingFunction()),
+          Map.entry("COALESCE", new CoalesceFunction()),
           Map.entry("FACT", new FactFunction()),
           Map.entry("FLOOR", new FloorFunction()),
           Map.entry("IF", new IfFunction()),

diff --git a/src/main/java/com/ezylang/evalex/functions/basic/CoalesceFunction.java b/src/main/java/com/ezylang/evalex/functions/basic/CoalesceFunction.java
@@ -0,0 +1,40 @@
+/*
+  Copyright 2012-2022 Udo Klimaschewski
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+      http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+*/
+package com.ezylang.evalex.functions.basic;
+
+import com.ezylang.evalex.Expression;
+import com.ezylang.evalex.data.EvaluationValue;
+import com.ezylang.evalex.functions.AbstractFunction;
+import com.ezylang.evalex.functions.FunctionParameter;
+import com.ezylang.evalex.parser.Token;
+
+/**
+ * Returns the first non-null parameter, or {@link EvaluationValue#nullValue()} if all parameters
+ * are null.
+ */
+@FunctionParameter(name = "value", isVarArg = true)
+public class CoalesceFunction extends AbstractFunction {
+  @Override
+  public EvaluationValue evaluate(
+      Expression expression, Token functionToken, EvaluationValue... parameterValues) {
+    for (EvaluationValue parameter : parameterValues) {
+      if (!parameter.isNullValue()) {
+        return parameter;
+      }
+    }
+    return EvaluationValue.nullValue();
+  }
+}
diff --git a/src/test/java/com/ezylang/evalex/functions/basic/BasicFunctionsTest.java b/src/test/java/com/ezylang/evalex/functions/basic/BasicFunctionsTest.java
@@ -22,6 +22,7 @@
 import com.ezylang.evalex.EvaluationException;
 import com.ezylang.evalex.Expression;
 import com.ezylang.evalex.config.ExpressionConfiguration;
+import com.ezylang.evalex.config.TestConfigurationProvider;
 import com.ezylang.evalex.data.EvaluationValue;
 import com.ezylang.evalex.parser.ParseException;
 import com.ezylang.evalex.parser.Token;
@@ -320,4 +321,31 @@ void testLog10Zero() {
         .isInstanceOf(EvaluationException.class)
         .hasMessage("Parameter must not be zero");
   }
+
+  @ParameterizedTest
+  @CsvSource(
+      delimiter = ':',
+      value = {
+        "COALESCE(null,1) : 1",
+        "COALESCE(null,\"abc\",1,null,2,3) : abc",
+        "COALESCE(1,null) : 1",
+        "COALESCE(null,null,null,null,1.1) : 1.1",
+        "COALESCE(null,null,null) :",
+        "COALESCE(null) :"
+      })
+  void testCoalesce(String expression, String expectedResult)
+      throws EvaluationException, ParseException {
+    EvaluationValue evaluationValue =
+        new Expression(
+                expression,
+                TestConfigurationProvider.StandardConfigurationWithAdditionalTestOperators)
+            .evaluate();
+
+    if (expectedResult == null) {
+      assertThat(evaluationValue.isNullValue()).isTrue();
+    } else {
+      assertThat(evaluationValue.isNullValue()).isFalse();
+      assertThat(evaluationValue.getStringValue()).isEqualTo(expectedResult);
+    }
+  }
 }