unique validation has to work on the model to have the correct snapshot of the data

src/main/java/ninja/javafx/smartcsv/fx/table/model/CSVModel.java

@@ -39,7 +39,7 @@ import org.apache.logging.log4j.Logger;
  * The CSVModel is the client representation for the csv filepath.
  * It holds the data in rows, stores the header and manages the validator.
  */
-public final class CSVModel {
+public final class CSVModel implements ColumnValueProvider {
 
     private static final Logger logger = LogManager.getLogger(CSVModel.class);
 
@@ -55,7 +55,7 @@ public final class CSVModel {
      * @param validationConfiguration the validator configuration for this data
      */
     public void setValidationConfiguration(ValidationConfiguration validationConfiguration) {
-        this.validator = new Validator(validationConfiguration);
+        this.validator = new Validator(validationConfiguration, this);
         revalidate();
     }
 
@@ -145,11 +145,19 @@ public final class CSVModel {
     public ValidationConfiguration createValidationConfiguration() {
         ValidationConfiguration newValidationConfiguration = new ValidationConfiguration();
         newValidationConfiguration.setHeaderNames(this.header);
-        this.validator = new Validator(newValidationConfiguration);
+        this.validator = new Validator(newValidationConfiguration, this);
         this.revalidate();
         return newValidationConfiguration;
     }
 
 
+    @Override
+    public String getValue(int row, String column) {
+        return rows.get(row).getColumns().get(column).getValue().getValue();
+    }
 
+    @Override
+    public int getNumberOfRows() {
+        return rows.size();
+    }
 }

src/main/java/ninja/javafx/smartcsv/fx/table/model/ColumnValueProvider.java

@@ -0,0 +1,11 @@
+package ninja.javafx.smartcsv.fx.table.model;
+
+/**
+ * interface for easier access to values in a column
+ */
+public interface ColumnValueProvider {
+
+    String getValue(int row, String column);
+    int getNumberOfRows();
+
+}

src/main/java/ninja/javafx/smartcsv/validation/UniqueValidation.java

@@ -25,26 +25,50 @@
 */
 package ninja.javafx.smartcsv.validation;
 
-import java.util.HashMap;
+import ninja.javafx.smartcsv.fx.table.model.ColumnValueProvider;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static java.util.Collections.sort;
+import static java.util.stream.Collectors.joining;
 
 /**
  * Checks if the value is unique in the column
  */
 public class UniqueValidation extends EmptyAllowedValidation {
 
-    private HashMap<String, Integer> columnValueMap = new HashMap<>();
+    private ColumnValueProvider columnValueProvider;
+    private String column;
+
+    public UniqueValidation(ColumnValueProvider columnValueProvider, String column) {
+        this.columnValueProvider = columnValueProvider;
+        this.column = column;
+    }
 
     @Override
     public void check(int row, String value, ValidationError error) {
-        Integer valueInLineNumber = columnValueMap.get(value);
-        if (valueInLineNumber != null) {
-            if (!valueInLineNumber.equals(row)) {
-                valueInLineNumber += 1; // show not 0 based line numbers to user
-                error.add("validation.message.uniqueness", value, valueInLineNumber.toString());
+
+        List<Integer> lineNumbers = new ArrayList<>();
+
+        int numberOfRows = columnValueProvider.getNumberOfRows();
+        for (int currentRowOfIteration = 0; currentRowOfIteration < numberOfRows; currentRowOfIteration++) {
+            String storedValue = columnValueProvider.getValue(currentRowOfIteration, column);
+
+            if (storedValue.equals(value) && currentRowOfIteration != row) {
+                lineNumbers.add(currentRowOfIteration + 1); // show not 0 based line numbers to user
             }
-        } else {
-            columnValueMap.put(value, row);
         }
+
+        if (!lineNumbers.isEmpty()) {
+            if (lineNumbers.size() > 1) {
+                sort(lineNumbers);
+                error.add("validation.message.uniqueness.multiple", value, lineNumbers.stream().map(Object::toString).collect(joining(", ")));
+            } else {
+                error.add("validation.message.uniqueness.single", value, lineNumbers.get(0).toString());
+            }
+        }
+
     }
 
     @Override

src/main/java/ninja/javafx/smartcsv/validation/Validator.java

@@ -26,6 +26,8 @@
 
 package ninja.javafx.smartcsv.validation;
 
+import ninja.javafx.smartcsv.fx.table.model.ColumnValueProvider;
+
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -41,6 +43,7 @@ public class Validator {
     ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 
     private ValidationConfiguration validationConfig;
+    private ColumnValueProvider columnValueProvider;
     private Map<String, Map<Validation.Type, Validation>> columnValidationMap = new HashMap<>();
 
     ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -52,8 +55,9 @@ public class Validator {
      *
      * @param validationConfig
      */
-    public Validator(ValidationConfiguration validationConfig) {
+    public Validator(ValidationConfiguration validationConfig, ColumnValueProvider columnValueProvider) {
         this.validationConfig = validationConfig;
+        this.columnValueProvider = columnValueProvider;
         initColumnValidations();
     }
 
@@ -160,7 +164,7 @@ public class Validator {
 
         Boolean uniqueRule = validationConfig.getUniqueRuleFor(column);
         if (uniqueRule != null && uniqueRule) {
-            add(column, new UniqueValidation());
+            add(column, new UniqueValidation(columnValueProvider, column));
         }
 
         String dateRule = validationConfig.getDateRuleFor(column);