Fix bus/breaker topology in case of no connected terminal present

java/src/main/java/com/powsybl/python/network/Dataframes.java

@@ -363,15 +363,9 @@ private static DataframeMapper<VoltageLevel.BusBreakerView, Void> createBusBreak
     }
 
     private static List<BusBreakerViewBusData> getBusBreakerViewBuses(VoltageLevel voltageLevel) {
-        return voltageLevel.getBusBreakerView().getBusStream().map(bus -> {
-            Bus busViewBus = bus.getConnectedTerminalStream()
-                    .map(t -> t.getBusView().getBus())
-                    .filter(Objects::nonNull)
-                    .findFirst()
-                    .orElse(null);
-            return new BusBreakerViewBusData(bus, busViewBus);
-        }).collect(Collectors.toList());
-
+        return voltageLevel.getBusBreakerView().getBusStream()
+                .map(bus -> new BusBreakerViewBusData(bus, NetworkUtil.getBusViewBus(bus)))
+                .toList();
     }
 
     private static DataframeMapper<VoltageLevel, Void> createBusBreakerViewBuses() {

java/src/main/java/com/powsybl/python/network/NetworkUtil.java

@@ -15,6 +15,7 @@
 
 import java.util.Collection;
 import java.util.List;
+import java.util.Objects;
 import java.util.Set;
 import java.util.function.Consumer;
 import java.util.function.Supplier;
@@ -246,4 +247,37 @@ public static String getRegulatedElementId(Supplier<Terminal> regulatingTerminal
         Terminal terminal = regulatingTerminalGetter.get();
         return terminal.getConnectable() != null ? terminal.getConnectable().getId() : null;
     }
+
+    /**
+     * @param b bus in Bus/Breaker view
+     * @return bus in bus view containing b if there is one, or null if none.
+     */
+    public static Bus getBusViewBus(Bus b) {
+        // First we try the fast and easy way using connected terminals. Works for the vast majority of buses.
+        Bus busInBusView = b.getConnectedTerminalStream().map(t -> t.getBusView().getBus())
+                .filter(Objects::nonNull)
+                .findFirst()
+                .orElse(null);
+        if (busInBusView != null) {
+            return busInBusView;
+        }
+        // Didn't find using connected terminals. There is the possibility that the bus has zero connected terminal
+        // on its own but is still part of a Merged Bus via a closed retained switch. We examine this case below.
+        VoltageLevel voltageLevel = b.getVoltageLevel();
+        if (voltageLevel.getTopologyKind() == TopologyKind.BUS_BREAKER) {
+            // Bus/Breaker. There is an easy method directly available.
+            return voltageLevel.getBusView().getMergedBus(b.getId());
+        } else {
+            // Node/Breaker. We should probably build something more efficient on powsybl-core side to avoid having
+            // to loop over all buses in the voltage level.
+            for (Bus bus : voltageLevel.getBusView().getBuses()) {
+                boolean found = voltageLevel.getBusBreakerView().getBusStreamFromBusViewBusId(bus.getId())
+                        .anyMatch(b2 -> b.getId().equals(b2.getId()));
+                if (found) {
+                    return bus;
+                }
+            }
+            return null;
+        }
+    }
 }

java/src/test/java/com/powsybl/python/network/NetworkUtilTest.java

@@ -7,15 +7,16 @@
  */
 package com.powsybl.python.network;
 
-import com.powsybl.iidm.network.Network;
+import com.powsybl.iidm.network.*;
 import com.powsybl.iidm.network.test.EurostagTutorialExample1Factory;
 import com.powsybl.python.commons.PyPowsyblApiHeader;
 import org.junit.jupiter.api.Test;
 
 import java.util.Collections;
 import java.util.List;
+import java.util.Map;
 
-import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.*;
 
 /**
  * @author Geoffroy Jamgotchian {@literal <geoffroy.jamgotchian at rte-france.com>}
@@ -28,4 +29,50 @@ void test() {
         List<String> elementsIds = NetworkUtil.getElementsIds(network, PyPowsyblApiHeader.ElementType.TWO_WINDINGS_TRANSFORMER, Collections.singleton(24.0), Collections.singleton("FR"), true, true, false);
         assertEquals(Collections.singletonList("NGEN_NHV1"), elementsIds);
     }
+
+    @Test
+    void testBusFromBusBreakerViewBus() {
+        Network network = createTopologyTestNetwork();
+        var expected = Map.of(
+            "B1", "VL1_0",
+            "B2", "VL1_0",
+            "B3", "",
+            "VL2_0", "VL2_0",
+            "VL2_1", "VL2_0",
+            "VL2_2", "");
+        expected.forEach((busBreakerBusId, busIdExpected) -> {
+            Bus bus = NetworkUtil.getBusViewBus(network.getBusBreakerView().getBus(busBreakerBusId));
+            if (!busIdExpected.isEmpty()) {
+                assertNotNull(bus);
+                assertEquals(busIdExpected, bus.getId());
+            } else {
+                assertNull(bus);
+            }
+        });
+    }
+
+    private static Network createTopologyTestNetwork() {
+        Network network = NetworkFactory.findDefault().createNetwork("test", "code");
+
+        var vl1 = network.newVoltageLevel().setTopologyKind(TopologyKind.BUS_BREAKER).setId("VL1").setNominalV(400.).add();
+        vl1.getBusBreakerView().newBus().setId("B1").add();
+        vl1.getBusBreakerView().newBus().setId("B2").add();
+        vl1.getBusBreakerView().newBus().setId("B3").add();
+        vl1.getBusBreakerView().newSwitch().setId("CB1.1").setOpen(false).setBus1("B1").setBus2("B2").add();
+        vl1.getBusBreakerView().newSwitch().setId("CB1.2").setOpen(true).setBus1("B1").setBus2("B2").add();
+        vl1.newLoad().setId("L1").setP0(10.).setQ0(3.).setConnectableBus("B1").setBus("B1").add();
+
+        var vl2 = network.newVoltageLevel().setTopologyKind(TopologyKind.NODE_BREAKER).setId("VL2").setNominalV(400.).add();
+        vl2.getNodeBreakerView().newBusbarSection().setId("BBS1").setNode(0).add();
+        vl2.getNodeBreakerView()
+                .newSwitch()
+                .setId("CB2.1").setOpen(false).setRetained(true).setKind(SwitchKind.BREAKER).setNode1(0).setNode2(1).add();
+        vl2.getNodeBreakerView()
+                .newSwitch()
+                .setId("CB2.2").setOpen(true).setRetained(true).setKind(SwitchKind.BREAKER).setNode1(1).setNode2(2).add();
+        vl2.newLoad().setId("L2").setP0(10.).setQ0(3.).setNode(3).add();
+        vl2.getNodeBreakerView().newInternalConnection().setNode1(0).setNode2(3).add();
+
+        return network;
+    }
 }

tests/test_network.py

@@ -1722,6 +1722,36 @@ def test_bus_breaker_view_draw_graph():
     plt.show()
 
 
+def test_bus_breaker_topology_no_connected_terminal():
+    n = pp.network.create_empty()
+    n.create_substations(id='S')
+
+    n.create_voltage_levels(id='VL1', substation_id='S', nominal_v=380, topology_kind='BUS_BREAKER')
+    n.create_buses(id='B1', voltage_level_id='VL1')
+    n.create_buses(id='B2', voltage_level_id='VL1')
+    n.create_buses(id='B3', voltage_level_id='VL1')
+    n.create_loads(id='L1', voltage_level_id='VL1', p0=0, q0=0, bus_id='B1', connectable_bus_id='B1')
+    n.create_switches(id='CB1.1', kind='BREAKER', voltage_level_id='VL1', bus1_id='B1', bus2_id='B2', open=False)
+    n.create_switches(id='CB1.2', kind='BREAKER', voltage_level_id='VL1', bus1_id='B2', bus2_id='B3', open=True)
+
+    n.create_voltage_levels(id='VL2', substation_id='S', nominal_v=380, topology_kind='NODE_BREAKER')
+    n.create_busbar_sections(id='BB', voltage_level_id='VL2', node=0)
+    n.create_switches(id='CB2.1', kind='BREAKER', voltage_level_id='VL2', node1=0, node2=1, open=False, retained=True)
+    n.create_switches(id='CB2.2', kind='BREAKER', voltage_level_id='VL2', node1=1, node2=2, open=True, retained=True)
+    n.create_switches(id='SW', kind='DISCONNECTOR', voltage_level_id='VL2', node1=0, node2=3, open=False)
+    n.create_loads(id='L2', voltage_level_id='VL2', p0=0, q0=0, node=3)
+
+    topo_vl1 = n.get_bus_breaker_topology('VL1').buses
+    assert 'VL1_0' == topo_vl1.loc['B1']['bus_id']
+    assert 'VL1_0' == topo_vl1.loc['B2']['bus_id']
+    assert '' == topo_vl1.loc['B3']['bus_id']
+
+    topo_vl2 = n.get_bus_breaker_topology('VL2').buses
+    assert 'VL2_0' == topo_vl2.loc['VL2_0']['bus_id']
+    assert 'VL2_0' == topo_vl2.loc['VL2_1']['bus_id']
+    assert '' == topo_vl2.loc['VL2_2']['bus_id']
+
+
 def test_dataframe_attributes_filtering():
     n = pp.network.create_eurostag_tutorial_example1_network()
     buses_selected_attributes = n.get_buses(attributes=['v_mag', 'voltage_level_id'])