--- a/backend/src/main/java/org/dive4elements/river/model/sinfo/DailyDischargeValue.java	Thu Aug 16 08:44:26 2018 +0200
+++ b/backend/src/main/java/org/dive4elements/river/model/sinfo/DailyDischargeValue.java	Thu Aug 16 08:47:41 2018 +0200
@@ -13,6 +13,8 @@
 import java.io.Serializable;
 import java.util.Date;
 import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
 
 import javax.persistence.Column;
 import javax.persistence.Entity;
@@ -27,7 +29,9 @@
 import org.dive4elements.river.backend.SessionHolder;
 import org.dive4elements.river.model.Gauge;
 import org.hibernate.Query;
+import org.hibernate.SQLQuery;
 import org.hibernate.Session;
+import org.hibernate.type.StandardBasicTypes;
 
 /**
  * Hibernate binding for the DB table daily_discharge_values
@@ -49,9 +53,6 @@
         DAY, DISCHARGE;
     }
 
-    public enum MinMax {
-        min, max
-    }
 
     /***** FIELDS *****/
 
@@ -65,6 +66,7 @@
 
     private Double discharge;
 
+
     /***** CONSTRUCTORS *****/
 
     public DailyDischargeValue() {
@@ -83,6 +85,7 @@
         this(dailyDischarge, day, Double.valueOf(discharge));
     }
 
+
     /***** METHODS *****/
 
     @Id
@@ -142,17 +145,62 @@
     /**
      * Selects from the database the daily discharge, puts the first and the last into a List (min, max day)
      */
-
-    public static Date getGlobalMinMax(final Gauge gauge, final MinMax minmax) {
+    public static Date[] getTimePeriod(final Gauge gauge, final Date fromDay, final Date toDay) {
         final Session session = SessionHolder.HOLDER.get();
-        final Query query = session.createQuery(
-                "SELECT " + minmax.toString() + "(v.day) " + " FROM DailyDischargeValue AS v JOIN v.dailyDischarge AS s" + " WHERE (s.gauge.id=:gaugeid)");
+        final Query query = session.createQuery("SELECT MIN(v.day), MAX(v.day)"
+                + " FROM DailyDischargeValue AS v JOIN v.dailyDischarge AS s"
+                + " WHERE (s.gauge.id=:gaugeid) AND (v.day BETWEEN :startDate AND :endDate)");
         query.setParameter("gaugeid", gauge.getId());
-        final List<Date> list = query.list();
-        if (list != null && list.size() == 1) {
-            return list.get(0);
+        query.setDate("startDate", fromDay);
+        query.setDate("endDate", toDay);
+        final List<Object[]> list = query.list();
+        if (!list.isEmpty()) {
+            return new Date[] { (Date) list.get(0)[0], (Date) list.get(0)[1] };
         }
         return null;
     }
 
+    /**
+     * Fetches a map of minimum+maximum daily discharge dates (or null) by gauge for a list of gauges and a time period
+     */
+    public static Map<Gauge, Date[]> fetchGaugesTimePeriod(final List<Gauge> gauges, final Date fromDay, final Date toDay) {
+        final Map<Gauge, Date[]> result = new TreeMap<>();
+        final Map<Integer, Gauge> gaugelookup = new TreeMap<>();
+        String gaugeids = "";
+        String sep = "";
+        for (final Gauge gauge : gauges) {
+            gaugeids += sep + gauge.getId().toString();
+            sep = ",";
+            result.put(gauge, null);
+            gaugelookup.put(gauge.getId(), gauge);
+        }
+        final Session session = SessionHolder.HOLDER.get();
+        final SQLQuery query = session.createSQLQuery("SELECT g.id AS gauge_id, MIN(v.day) AS min_day, MAX(v.day) AS max_day"
+                + "FROM (gauges g LEFT JOIN daily_discharge s ON g.id=s.gauge_id)"
+                + "  LEFT JOIN daily_discharge_values v ON s.id=v.daily_discharge_id"
+                + " WHERE g.id IN (:gaugeids)"
+                + "  AND v.day BETWEEN :fromDay AND :toDay"
+                + " GROUP BY g.id"
+                + "UNION SELECT id, NULL, NULL"
+                + "  FROM gauges"
+                + "  WHERE id IN (:gaugeids)"
+                + "   AND id NOT IN "
+                +"    (SELECT s2.gauge_id FROM daily_discharge s2 INNER JOIN daily_discharge_values v2 ON s2.id=v2.daily_discharge_id"
+                + "      WHERE v2.day BETWEEN :fromDay AND :toDay)"
+                + "ORDER BY 1")
+                .addScalar("gauge_id", StandardBasicTypes.INTEGER)
+                .addScalar("min_day", StandardBasicTypes.DATE)
+                .addScalar("max_day", StandardBasicTypes.DATE);
+        query.setString("gaugeids", gaugeids);
+        query.setDate("fromDay", fromDay);
+        query.setDate("toDay", toDay);
+        final List<Object[]> rows = query.list();
+        if (!rows.isEmpty()) {
+            // TODO handle nulls
+            for (int i = 0; i <= rows.size() - 1; i++)
+                result.put(gaugelookup.get(rows.get(i)[0]), new Date[] { (Date) rows.get(i)[1], (Date) rows.get(i)[2] });
+            return result;
+        }
+        return new TreeMap<>();
+    }
 }