Consider query columns as property names.

Query columns now get checked against property names.
If such a property name is found, the property is used.
Otherwise the column is considered a literal column and used as is in the SQL generation.

Original pull request #1967
See #1803

Author: schauder

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/convert/SqlGenerator.java

@@ -541,24 +541,25 @@ private Projection getProjection(Collection<SqlIdentifier> keyColumns, Query que
 
 		if (!CollectionUtils.isEmpty(query.getColumns())) {
 			for (SqlIdentifier columnName : query.getColumns()) {
-				columns.add(Column.create(columnName, table));
+
+				String columnNameString = columnName.getReference();
+				RelationalPersistentProperty property = entity.getPersistentProperty(columnNameString);
+				if (property != null) {
+
+					AggregatePath aggregatePath = mappingContext.getAggregatePath(
+							mappingContext.getPersistentPropertyPath(columnNameString, entity.getTypeInformation()));
+					gatherColumn(aggregatePath, joins, columns);
+				} else {
+					columns.add(Column.create(columnName, table));
+				}
 			}
 		} else {
 			for (PersistentPropertyPath<RelationalPersistentProperty> path : mappingContext
 					.findPersistentPropertyPaths(entity.getType(), p -> true)) {
 
-				AggregatePath extPath = mappingContext.getAggregatePath(path);
+				AggregatePath aggregatePath = mappingContext.getAggregatePath(path);
 
-				// add a join if necessary
-				Join join = getJoin(extPath);
-				if (join != null) {
-					joins.add(join);
-				}
-
-				Column column = getColumn(extPath);
-				if (column != null) {
-					columns.add(column);
-				}
+				gatherColumn(aggregatePath, joins, columns);
 			}
 		}
 
@@ -569,6 +570,20 @@ private Projection getProjection(Collection<SqlIdentifier> keyColumns, Query que
 		return new Projection(columns, joins);
 	}
 
+	private void gatherColumn(AggregatePath aggregatePath, Set<Join> joins, Set<Expression> columns) {
+
+		// add a join if necessary
+		Join join = getJoin(aggregatePath);
+		if (join != null) {
+			joins.add(join);
+		}
+
+		Column column = getColumn(aggregatePath);
+		if (column != null) {
+			columns.add(column);
+		}
+	}
+
 	/**
 	 * Projection including its source joins.
 	 *

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/core/convert/SqlGeneratorUnitTests.java

@@ -373,7 +373,7 @@ void selectByQueryWithColumnLimit() {
 		String sql = sqlGenerator.selectByQuery(query, new MapSqlParameterSource());
 
 		assertThat(sql).contains( //
-				"SELECT dummy_entity.id1, dummy_entity.alpha, dummy_entity.beta, dummy_entity.gamma", //
+				"SELECT dummy_entity.id1 AS id1, dummy_entity.alpha, dummy_entity.beta, dummy_entity.gamma", //
 				"FROM dummy_entity" //
 		);
 	}