Fix #142

release-notes/CREDITS

@@ -97,3 +97,8 @@ George Fraser (georgewfraser@github)
 * Contributed #127: Add `CsvGenerator.Feature.ALWAYS_QUOTE_EMPTY_STRINGS` to allow forced
   quoting of empty Strings.
  (2.9.0)
+
+Austin Sharp (sharpau@github)
+
+* Suggested #142: Add methods for appending columns of a `CsvSchema` into another
+ (2.9.0)

release-notes/VERSION

@@ -12,7 +12,9 @@ Project: jackson-dataformat-csv
 #130: Add fluent addColumns operation to CsvSchema.Builder
  (contributed by Peter A)
 #139: Add `CsvParser.Feature.ALLOW_TRAILING_COMMA` to allow enforcing strict handling
-  (contributed by Nick B)
+ (contributed by Nick B)
+#142: Add methods for appending columns of a `CsvSchema` into another
+ (suggested by Austin S)
 
 2.8.6 (12-Jan-2017)
 2.8.5 (14-Nov-2016)

src/main/java/com/fasterxml/jackson/dataformat/csv/CsvSchema.java

@@ -453,21 +453,37 @@ public Builder(CsvSchema src)
             _anyPropertyName = src._anyPropertyName;
         }
 
+        /**
+         * NOTE: does NOT check for duplicate column names so it is possibly to
+         * accidentally add duplicates.
+         */
         public Builder addColumn(String name) {
             int index = _columns.size();
             return addColumn(new Column(index, name));
         }
+
+        /**
+         * NOTE: does NOT check for duplicate column names so it is possibly to
+         * accidentally add duplicates.
+         */
         public Builder addColumn(String name, ColumnType type) {
             int index = _columns.size();
             return addColumn(new Column(index, name, type));
         }
 
+        /**
+         * NOTE: does NOT check for duplicate column names so it is possibly to
+         * accidentally add duplicates.
+         */
         public Builder addColumn(Column c) {
             _columns.add(c);
             return this;
         }
 
         /**
+         * NOTE: does NOT check for duplicate column names so it is possibly to
+         * accidentally add duplicates.
+         *
          * @since 2.9
          */
         public Builder addColumns(Iterable<Column> cs) {
@@ -478,6 +494,9 @@ public Builder addColumns(Iterable<Column> cs) {
         }
 
         /**
+         * NOTE: does NOT check for duplicate column names so it is possibly to
+         * accidentally add duplicates.
+         *
          * @since 2.9
          */
         public Builder addColumns(Iterable<String> names, ColumnType type) {
@@ -488,6 +507,24 @@ public Builder addColumns(Iterable<String> names, ColumnType type) {
             return result;
         }
 
+        /**
+         * NOTE: unlike many other add methods, this method DOES check for, and
+         * discard, possible duplicate columns: that is, if this builder already
+         * has a column with same name as column to be added, existing column
+         * is retained and new column ignored.
+         *
+         * @since 2.9
+         */
+        public Builder addColumnsFrom(CsvSchema schema) {
+            Builder result = this;
+            for (Column col : schema) {
+                if (!hasColumn(col.getName())) {
+                    result = result.addColumn(col);
+                }
+            }
+            return result;
+        }
+
         public Builder addArrayColumn(String name) {
             int index = _columns.size();
             return addColumn(new Column(index, name, ColumnType.ARRAY, ""));
@@ -577,7 +614,25 @@ public int size() {
         public Iterator<Column> getColumns() {
             return _columns.iterator();
         }
-
+
+        /**
+         *<p>
+         * NOTE: this method requires linear scan over existing columns
+         * so it may be more efficient to use other types of lookups if
+         * available (for example, {@link CsvSchema#column(String)} has a
+         * hash lookup to use).
+         *
+         * @since 2.9
+         */
+        public boolean hasColumn(String name) {
+            for (int i = 0, end = _columns.size(); i < end; ++i) {
+                if (_columns.get(i).getName().equals(name)) {
+                    return true;
+                }
+            }
+            return false;
+        }
+
         /**
          * Method for specifying whether Schema should indicate that
          * a header line (first row that contains column names) is to be
@@ -1114,10 +1169,7 @@ public CsvSchema withoutEscapeChar() {
      */
     @Deprecated // in 2.7; remove in 2.8
     public CsvSchema withArrayElementSeparator(char c) {
-        return (Character.toString(c).equals(_arrayElementSeparator)) ? this
-                : new CsvSchema(_columns, _features,
-                        _columnSeparator, _quoteChar, _escapeChar, _lineSeparator, Character.toString(c),
-                        _nullValue, _columnsByName, _anyPropertyName);
+        return withArrayElementSeparator( Character.toString(c));
     }
 
     /**
@@ -1157,13 +1209,40 @@ public CsvSchema withNullValue(String nvl) {
                 (nvl == null) ? null : nvl.toCharArray(),
                 _columnsByName, _anyPropertyName);
     }
-    
+
     public CsvSchema withoutColumns() {
         return new CsvSchema(NO_COLUMNS, _features,
                 _columnSeparator, _quoteChar, _escapeChar, _lineSeparator, _arrayElementSeparator,
                 _nullValue, _columnsByName, _anyPropertyName);
     }
 
+    /**
+     * Mutant factory method that will try to combine columns of this schema with those
+     * from `toAppend`, starting with columns of this instance, and ignoring
+     * duplicates (if any) from argument `toAppend`.
+     * All settings aside from column sets are copied from `this` instance.
+     *<p>
+     * As with all `withXxx()` methods this method never modifies `this` but either
+     * returns it unmodified (if no new columns found from `toAppend`), or constructs
+     * a new instance and returns that.
+     *
+     * @since 2.9
+     */
+    public CsvSchema withColumnsFrom(CsvSchema toAppend) {
+        int addCount = toAppend.size();
+        if (addCount == 0) {
+            return this;
+        }
+        Builder b = rebuild();
+        for (int i = 0; i < addCount; ++i) {
+            Column col = toAppend.column(i);
+            if (column(col.getName()) == null) {
+                b.addColumn(col);
+            }
+        }
+        return b.build();
+    }
+
     /**
      * @since 2.7
      */
@@ -1318,9 +1397,20 @@ public String getNullValueString() {
     public Iterator<Column> iterator() {
         return Arrays.asList(_columns).iterator();
     }
-
+
+    /**
+     * Accessor for finding out how many columns this schema defines.
+     *
+     * @return Number of columns this schema defines
+     */
     public int size() { return _columns.length; }
-
+
+    /**
+     * Accessor for column at specified index (0-based); index having to be within
+     *<pre>
+     *    0 &lt;= index &lt; size()
+     *</pre>
+     */
     public Column column(int index) {
         return _columns[index];
     }

src/test/java/com/fasterxml/jackson/dataformat/csv/schema/SchemaTest.java

@@ -22,14 +22,25 @@ static class ArrayWrapper {
         public List<String> c;
     }
 
-    // for [databind#74]
+    // for [dataformat-csv#74]
     static class Point {
         public int y;
         public int x;
     }
 
     @JsonPropertyOrder()
     public static class PointWithAnnotation extends Point {}
+
+    // for [dataformat-csv#142]
+    interface Named {
+        public String getFirstName();
+        public String getLastName();
+    }
+
+    static abstract class YZ {
+        public abstract int getY();
+        public abstract int getZ();
+    }
 
     /*
     /**********************************************************************
@@ -133,7 +144,7 @@ private void _verifyLinks(CsvSchema schema)
             prev = curr;
         }
     }
-    
+
     // For [dataformat-csv#74]: problems applying default do-sort handling
     public void testSchemaWithOrdering() throws Exception
     {
@@ -158,4 +169,41 @@ public void testSchemaWithReordering()
         CsvSchema schemaWithoutReordering = schemaWithReordering.withColumnReordering(false);
         assertFalse(schemaWithoutReordering.reordersColumns());
     }
+
+    // For [dataformat-csv#142]: append columns from POJOs
+    public void testSchemaComposition() throws Exception
+    {
+        CsvSchema pointSchema = MAPPER.typedSchemaFor(Point.class);
+        CsvSchema yzSchema = MAPPER.typedSchemaFor(YZ.class);
+        CsvSchema namedSchema = MAPPER.typedSchemaFor(Named.class);
+
+        // should only add `z` since there's already `y`
+        CsvSchema schema = pointSchema;
+        schema = schema.withColumnsFrom(yzSchema);
+        // but then two name properties
+        schema = schema.withColumnsFrom(namedSchema);
+
+        assertEquals(5, schema.size());
+        Iterator<CsvSchema.Column> it = schema.iterator();
+        assertEquals("x", it.next().getName());
+        assertEquals("y", it.next().getName());
+        assertEquals("z", it.next().getName());
+        assertEquals("firstName", it.next().getName());
+        assertEquals("lastName", it.next().getName());
+
+        // and try alternate way as well.
+        CsvSchema.Builder builder = CsvSchema.builder();
+        builder.addColumnsFrom(yzSchema)
+            .addColumnsFrom(namedSchema)
+            .addColumnsFrom(pointSchema);
+        schema = builder.build();
+
+        assertEquals(5, schema.size());
+        it = schema.iterator();
+        assertEquals("y", it.next().getName());
+        assertEquals("z", it.next().getName());
+        assertEquals("firstName", it.next().getName());
+        assertEquals("lastName", it.next().getName());
+        assertEquals("x", it.next().getName());
+    }
 }