Store sharded tables in a map

Author: jeffgbutler

src/test/java/examples/sharding/ShardingTest.java

@@ -26,6 +26,8 @@
 import java.io.InputStreamReader;
 import java.sql.Connection;
 import java.sql.DriverManager;
+import java.util.HashMap;
+import java.util.Map;
 
 import examples.sharding.TableCodesDynamicSqlSupport.TableCodes;
 import org.apache.ibatis.datasource.unpooled.UnpooledDataSource;
@@ -45,9 +47,11 @@
 class ShardingTest {
     private static final String JDBC_URL = "jdbc:hsqldb:mem:aname";
     private static final String JDBC_DRIVER = "org.hsqldb.jdbcDriver";
+    private final Map<String, TableCodes> shards = new HashMap<>();
 
     private SqlSessionFactory sqlSessionFactory;
 
+
     @BeforeEach
     void setup() throws Exception {
         Class.forName(JDBC_DRIVER);
@@ -151,16 +155,14 @@ private SelectStatementProvider buildSelect(int id) {
     }
 
     private TableCodes calculateTable(int id) {
-        // it might be better to lookup instances in a Map rather than creating a new instance
-        // every time
-        return tableCodes.withName(calculateTableName(id));
-    }
-
-    private String calculateTableName(int id) {
         if (id % 2 == 0) {
-            return "tableCodes_even";
+            return shards.computeIfAbsent("even", this::newTableInstance);
         } else {
-            return "tableCodes_odd";
+            return shards.computeIfAbsent("odd", this::newTableInstance);
         }
     }
+
+    private TableCodes newTableInstance(String suffix) {
+        return tableCodes.withName("tableCodes_" + suffix);
+    }
 }

src/test/kotlin/examples/kotlin/mybatis3/sharding/KShardingTest.kt

@@ -29,6 +29,7 @@ import org.mybatis.dynamic.sql.util.kotlin.mybatis3.select
 @TestInstance(TestInstance.Lifecycle.PER_CLASS)
 class KShardingTest {
     private lateinit var sqlSessionFactory: SqlSessionFactory
+    private val shards = mutableMapOf<String, KTableCodesTableDynamicSQLSupport.TableCodes>()
 
     @BeforeAll
     fun setup() {
@@ -131,13 +132,12 @@ class KShardingTest {
         return selectOneString(selectStatement)
     }
 
-    private fun calculateTable(id: Int) = tableCodes.withName(calculateTableName(id))
-
-    private fun calculateTableName(id: Int): String {
-        return if (id.mod(2) == 0) {
-            "tableCodes_even"
+    private fun calculateTable(id: Int) =
+        if (id % 2 == 0) {
+            shards.computeIfAbsent("even", this::newTableInstance)
         } else {
-            "tableCodes_odd"
+            shards.computeIfAbsent("odd", this::newTableInstance)
         }
-    }
+
+    private fun newTableInstance(suffix: String)= tableCodes.withName("tableCodes_$suffix")
 }