Add field metadata to query result object

Refactored the way rows are built in the native bindings which should
result in a small performance improvement

Author: brianc

lib/native/index.js

@@ -171,6 +171,10 @@ var clientBuilder = function(config) {
     connection._pulseQueryQueue(true);
   });
 
+  connection.on('_rowDescription', function(rowDescription) {
+    connection._activeQuery.handleRowDescription(rowDescription);
+  });
+
   //proxy some events to active query
   connection.on('_row', function(row) {
     connection._activeQuery.handleRow(row);

lib/native/query.js

@@ -22,6 +22,7 @@ var NativeQuery = function(config, values, callback) {
   this.callback = c.callback;
 
   this._result = new Result();
+  this._addedFields = false;
   //normalize values
   if(this.values) {
     for(var i = 0, len = this.values.length; i < len; i++) {
@@ -39,13 +40,35 @@ var mapRowData = function(row) {
   for(var i = 0, len = row.length; i < len; i++) {
     var item = row[i];
     result[item.name] = item.value === null ? null :
-      types.getTypeParser(item.type, 'text')(item.value);
+      types.getTypeParser(item.dataTypeID, 'text')(item.value);
   }
   return result;
 };
 
+NativeQuery.prototype.handleRowDescription = function(rowDescription) {
+  //multiple query statements in 1 action can result in multiple sets
+  //of rowDescriptions...eg: 'select NOW(); select 1::int;'
+  if(this._result.fields.length) {
+    this._result.fields = [];
+  }
+  for(var i = 0, len = rowDescription.length; i < len; i++) {
+    this._result.addField(rowDescription[i]);
+  }
+};
+
 NativeQuery.prototype.handleRow = function(rowData) {
-  var row = mapRowData(rowData);
+  var row = {};
+  for(var i = 0, len = rowData.length; i < len; i++) {
+    var rawValue = rowData[i];
+    var field = this._result.fields[i];
+    var fieldType = field.dataTypeID;
+    var parsedValue = null;
+    if(rawValue !== null) {
+      parsedValue = types.getTypeParser(fieldType, 'text')(rawValue);
+    }
+    var fieldName = field.name;
+    row[fieldName] = parsedValue;
+  }
   if(this.callback) {
     this._result.addRow(row);
   }

src/binding.cc

@@ -61,7 +61,7 @@ class Connection : public ObjectWrap {
     routine_symbol = NODE_PSYMBOL("routine");
     name_symbol = NODE_PSYMBOL("name");
     value_symbol = NODE_PSYMBOL("value");
-    type_symbol = NODE_PSYMBOL("type");
+    type_symbol = NODE_PSYMBOL("dataTypeID");
     channel_symbol = NODE_PSYMBOL("channel");
     payload_symbol = NODE_PSYMBOL("payload");
     command_symbol = NODE_PSYMBOL("command");
@@ -522,13 +522,41 @@ class Connection : public ObjectWrap {
     }
     return false;
   }
+
+  //maps the postgres tuple results to v8 objects
+  //and emits row events
+  //TODO look at emitting fewer events because the back & forth between
+  //javascript & c++ might introduce overhead (requires benchmarking)
+  void EmitRowDescription(const PGresult* result)
+  {
+    HandleScope scope;
+    Local<Array> row = Array::New();
+    int fieldCount = PQnfields(result);
+    for(int fieldNumber = 0; fieldNumber < fieldCount; fieldNumber++) {
+      Local<Object> field = Object::New();
+      //name of field
+      char* fieldName = PQfname(result, fieldNumber);
+      field->Set(name_symbol, String::New(fieldName));
+
+      //oid of type of field
+      int fieldType = PQftype(result, fieldNumber);
+      field->Set(type_symbol, Integer::New(fieldType));
+
+      row->Set(Integer::New(fieldNumber), field);
+    }
+
+    Handle<Value> e = (Handle<Value>)row;
+    Emit("_rowDescription", &e);
+  }
+
   bool HandleResult(PGresult* result)
   {
     TRACE("PQresultStatus");
     ExecStatusType status = PQresultStatus(result);
     switch(status) {
     case PGRES_TUPLES_OK:
       {
+        EmitRowDescription(result);
         HandleTuplesResult(result);
         EmitCommandMetaData(result);
         return true;
@@ -592,24 +620,14 @@ class Connection : public ObjectWrap {
       Local<Array> row = Array::New();
       int fieldCount = PQnfields(result);
       for(int fieldNumber = 0; fieldNumber < fieldCount; fieldNumber++) {
-        Local<Object> field = Object::New();
-        //name of field
-        char* fieldName = PQfname(result, fieldNumber);
-        field->Set(name_symbol, String::New(fieldName));
-
-        //oid of type of field
-        int fieldType = PQftype(result, fieldNumber);
-        field->Set(type_symbol, Integer::New(fieldType));
 
         //value of field
         if(PQgetisnull(result, rowNumber, fieldNumber)) {
-          field->Set(value_symbol, Null());
+          row->Set(Integer::New(fieldNumber), Null());
         } else {
           char* fieldValue = PQgetvalue(result, rowNumber, fieldNumber);
-          field->Set(value_symbol, String::New(fieldValue));
+          row->Set(Integer::New(fieldNumber), String::New(fieldValue));
         }
-
-        row->Set(Integer::New(fieldNumber), field);
       }
 
       Handle<Value> e = (Handle<Value>)row;

test/integration/client/row-description-on-results-tests.js

@@ -0,0 +1,37 @@
+var helper = require('./test-helper');
+
+var Client = helper.Client;
+
+var conInfo = helper.config;
+
+var checkResult = function(result) {
+  assert(result.fields);
+  assert.equal(result.fields.length, 3);
+  var fields = result.fields;
+  assert.equal(fields[0].name, 'now');
+  assert.equal(fields[1].name, 'num');
+  assert.equal(fields[2].name, 'texty');
+  assert.equal(fields[0].dataTypeID, 1184);
+  assert.equal(fields[1].dataTypeID, 23);
+  assert.equal(fields[2].dataTypeID, 25);
+};
+
+test('row descriptions on result object', function() {
+  var client = new Client(conInfo);
+  client.connect(assert.success(function() {
+    client.query('SELECT NOW() as now, 1::int as num, $1::text as texty', ["hello"], assert.success(function(result) {
+      checkResult(result);
+      client.end();
+    }));
+  }));
+});
+
+test('row description on no rows', function() {
+  var client = new Client(conInfo);
+  client.connect(assert.success(function() {
+    client.query('SELECT NOW() as now, 1::int as num, $1::text as texty LIMIT 0', ["hello"], assert.success(function(result) {
+      checkResult(result);
+      client.end();
+    }));
+  }));
+});