Show example on how to implement SUM in Word

Using navigation expression we can iterate over all elements perform SUM aggregation over a property/field.

Author: zapov

Intermediate/WordTables/Readme.md

@@ -34,7 +34,7 @@ alias can be defined like products = groups:sort(usage).products:filter(active)
 
 and tag can look like `[[products.name]]` with all the behavior which was implicitly defined
 
-Here, navigation was used to take top N elements from the result set in an idiomatic way. 
+Here, navigation was used to take top N elements from the result set in an idiomatic way and for implementing Sum over existing field as `[[Fixed:Sum(Price)]]`
 
 ### merge-nulls/span-nulls metadata
 

Intermediate/WordTables/result.docx

@@ -118,6 +118,21 @@ static object LimitDataTable(object parent, object value, string member, string
 			return dt;
 		}
 
+		static object SumExpression(object parent, object value, string member, string metadata)
+		{
+			var arr = value as object[];
+			//check if plugin is applicable
+			if (arr == null || !metadata.StartsWith("Sum(")) return value;
+			if (arr.Length == 0 || arr.Contains(null)) return 0;
+			var signature = arr[0].GetType();
+			var propertyName = metadata.Substring(4, metadata.Length - 5);
+			var property = signature.GetField(propertyName);
+			var result = (decimal)0;
+			foreach (var el in arr)
+				result += (decimal)property.GetValue(el);
+			return result;
+		}
+
 		public static void Main(string[] args)
 		{
 			File.Copy("template/Tables.docx", "WordTables.docx", true);
@@ -139,6 +154,7 @@ public static void Main(string[] args)
 				.NavigateSeparator(':', null)
 				.Include(LimitDataTable)
 				.Include(CollapseNonEmpty)
+				.Include(SumExpression)
 				.Build();
 			var dynamicResize1 = new object[7, 3]{
 				{"a", "b", "c"},

Intermediate/WordTables/src/Program.cs

@@ -5,6 +5,7 @@
 
 import java.awt.Desktop;
 import java.io.*;
+import java.lang.reflect.Field;
 import java.math.BigDecimal;
 import java.sql.ResultSet;
 import java.sql.ResultSetMetaData;
@@ -88,6 +89,7 @@ public static void main(final String[] args) throws Exception {
                         .navigateSeparator(':', null)
                         .include(new LimitResultSet())
                         .include(new CollapseNonEmpty())
+                        .include(new SumExpression())
                         .build().open(templateStream, "docx", fos);
         tpl.process(arguments);
         tpl.close();
@@ -155,6 +157,29 @@ public Object navigate(Object parent, Object value, String member, String metada
         }
     }
 
+    static class SumExpression implements DocumentFactoryBuilder.Navigate {
+        @Override
+        public Object navigate(Object parent, Object value, String member, String metadata) {
+            //check if plugin is applicable
+            if (value instanceof List == false || !metadata.startsWith("Sum(")) return value;
+            List arr = (List) value;
+            if (arr.isEmpty() || arr.contains(null)) return 0;
+            String propertyName = metadata.substring(4, metadata.length() - 1);
+            Class<?> signature = arr.get(0).getClass();
+            BigDecimal result = BigDecimal.ZERO;
+            try {
+                Field property = signature.getField(propertyName);
+                for (Object el : arr) {
+                    BigDecimal f = (BigDecimal) property.get(el);
+                    result = result.add(f);
+                }
+            } catch (NoSuchFieldException | IllegalAccessException e) {
+                throw new RuntimeException(e);
+            }
+            return result;
+        }
+    }
+
     static class Limit10Table implements DocumentFactoryBuilder.Processor<ResultSet> {
         @Override
         public boolean tryProcess(String prefix, Templater templater, ResultSet resultSet) {