docs: simplify dialect detection for MyBatis sample (#1739)

Author: olavloite

samples/spring-data-mybatis/src/main/java/com/google/cloud/spanner/sample/JdbcConfiguration.java

@@ -16,55 +16,22 @@
 
 package com.google.cloud.spanner.sample;
 
-import com.google.cloud.spanner.jdbc.JdbcSqlException;
-import com.google.rpc.Code;
-import java.util.Objects;
+import com.google.cloud.spanner.jdbc.CloudSpannerJdbcConnection;
 import org.springframework.context.annotation.Configuration;
-import org.springframework.dao.DataAccessException;
-import org.springframework.dao.IncorrectResultSizeDataAccessException;
+import org.springframework.jdbc.core.ConnectionCallback;
 import org.springframework.jdbc.core.JdbcOperations;
 
 @Configuration
 public class JdbcConfiguration {
 
   /** Returns true if the current database is a Cloud Spanner PostgreSQL database. */
   public static boolean isCloudSpannerPG(JdbcOperations operations) {
-    try {
-      Long value =
-          operations.queryForObject(
-              "select 1 "
-                  + "from information_schema.database_options "
-                  + "where schema_name='public' "
-                  + "and option_name='database_dialect' "
-                  + "and option_value='POSTGRESQL'",
-              Long.class);
-      // Shouldn't really be anything else than 1 if the query succeeded, but this avoids complaints
-      // from the compiler.
-      if (Objects.equals(1L, value)) {
-        return true;
-      }
-    } catch (IncorrectResultSizeDataAccessException exception) {
-      // This indicates that it is a valid Cloud Spanner database, but not one that uses the
-      // PostgreSQL dialect.
-      throw new RuntimeException(
-          "The selected Cloud Spanner database does not use the PostgreSQL dialect");
-    } catch (DataAccessException exception) {
-      if (exception.getCause() instanceof JdbcSqlException) {
-        JdbcSqlException jdbcSqlException = (JdbcSqlException) exception.getCause();
-        if (jdbcSqlException.getCode() == Code.PERMISSION_DENIED
-            || jdbcSqlException.getCode() == Code.NOT_FOUND) {
-          throw new RuntimeException(
-              "Failed to get the dialect of the Cloud Spanner database. "
-                  + "Please check that the selected database exists and that you have permission to access it. "
-                  + "Cause: "
-                  + exception.getCause().getMessage(),
-              exception.getCause());
-        }
-      }
-      // ignore and fall through
-    } catch (Throwable exception) {
-      // ignore and fall through
-    }
-    return false;
+    return Boolean.TRUE.equals(
+        operations.execute(
+            (ConnectionCallback<Boolean>)
+                connection ->
+                    connection.isWrapperFor(CloudSpannerJdbcConnection.class)
+                        && com.google.cloud.spanner.Dialect.POSTGRESQL.equals(
+                            connection.unwrap(CloudSpannerJdbcConnection.class).getDialect())));
   }
 }

samples/spring-data-mybatis/src/test/java/com/google/cloud/spanner/sample/ApplicationTest.java

@@ -876,7 +876,7 @@ public void testRunApplication() {
     Application.main(new String[] {});
 
     assertEquals(
-        40,
+        39,
         mockSpanner.getRequestsOfType(ExecuteSqlRequest.class).stream()
             .filter(
                 request ->