Github user kaspersorensen commented on a diff in the pull request:
https://github.com/apache/metamodel/pull/85#discussion_r49314038
--- Diff: core/src/main/java/org/apache/metamodel/query/ConcatFunction.java
---
@@ -0,0 +1,79 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you 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 org.apache.metamodel.query;
+
+import org.apache.metamodel.data.Row;
+import org.apache.metamodel.schema.Column;
+import org.apache.metamodel.schema.ColumnType;
+import org.apache.metamodel.util.CollectionUtils;
+import org.apache.metamodel.util.Predicate;
+
+import java.util.List;
+
+/**
+ * Represents a function that concatenates values.
+ */
+public final class ConcatFunction extends DefaultScalarFunction {
+
+ @Override
+ public Object evaluate(Row row, Object[] parameters, SelectItem
operandItem) {
+ SelectItem[] selectItems = row.getSelectItems();
+ if (parameters.length == 0) {
+ throw new IllegalArgumentException("Expecting some parameters
to CONCAT function");
+ }
+ StringBuilder strBuilder = new StringBuilder();
+ for (Object parameter: parameters) {
+ String parameterAsString = parameter.toString();
--- End diff --
What I mean is that a few lines lower, starting with the ```if``` and
eventually hitting the ```getColumnValueFromRow``` (line 48) the parameter is
treated only as a string. But what would be more natural to me is to check what
type the parameter is. I think the parameter will already be a SelectItem here
actually, but it's being changed into a string via the ```toString()``` call
and then converted/resolved into a column by the ```getColumnValueFromRow```
call. It would be way better (IMO) to have something like:
```
final String valueToConcat;
if (parameter instanceof SelectItem) {
valueToConcat = row.getValue((SelectItem)parameter);
} else if (parameter instanceof Column) {
valueToConcat = row.getValue((Column)parameter);
} else {
valueToConcat = parameter;
}
strBuilder.append(valueToConcat);
```
And then you can delete the complete ```getColumnValueFromRow``` method
which is just making things quite complex I think.
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