add Mysql2::Client#fields method

ext/mysql2_ext.c

@@ -453,6 +453,8 @@ static VALUE rb_mysql_result_to_obj(MYSQL_RES * r) {
   wrapper->lastRowProcessed = 0;
   wrapper->resultFreed = 0;
   wrapper->result = r;
+  wrapper->fields = Qnil;
+  wrapper->rows = Qnil;
   rb_obj_call_init(obj, 0, NULL);
   return obj;
 }
@@ -481,6 +483,60 @@ static void rb_mysql_result_mark(void * wrapper) {
     }
 }
 
+static VALUE rb_mysql_result_fetch_field(mysql2_result_wrapper * wrapper, unsigned int idx, short int symbolize_keys) {
+  if (wrapper->fields == Qnil) {
+    wrapper->numberOfFields = mysql_num_fields(wrapper->result);
+    wrapper->fields = rb_ary_new2(wrapper->numberOfFields);
+  }
+
+  VALUE rb_field = rb_ary_entry(wrapper->fields, idx);
+  if (rb_field == Qnil) {
+    MYSQL_FIELD *field = NULL;
+  #ifdef HAVE_RUBY_ENCODING_H
+    rb_encoding *default_internal_enc = rb_default_internal_encoding();
+  #endif
+
+    field = mysql_fetch_field_direct(wrapper->result, idx);
+    if (symbolize_keys) {
+      char buf[field->name_length+1];
+      memcpy(buf, field->name, field->name_length);
+      buf[field->name_length] = 0;
+      rb_field = ID2SYM(rb_intern(buf));
+    } else {
+      rb_field = rb_str_new(field->name, field->name_length);
+  #ifdef HAVE_RUBY_ENCODING_H
+      rb_enc_associate(rb_field, utf8Encoding);
+      if (default_internal_enc) {
+        rb_field = rb_str_export_to_enc(rb_field, default_internal_enc);
+      }
+  #endif
+    }
+    rb_ary_store(wrapper->fields, idx, rb_field);
+  }
+
+  return rb_field;
+}
+
+static VALUE rb_mysql_result_fetch_fields(VALUE self) {
+  mysql2_result_wrapper * wrapper;
+  unsigned int i = 0;
+
+  GetMysql2Result(self, wrapper);
+
+  if (wrapper->fields == Qnil) {
+    wrapper->numberOfFields = mysql_num_fields(wrapper->result);
+    wrapper->fields = rb_ary_new2(wrapper->numberOfFields);
+  }
+
+  if (RARRAY_LEN(wrapper->fields) != wrapper->numberOfFields) {
+    for (i=0; i<wrapper->numberOfFields; i++) {
+      rb_mysql_result_fetch_field(wrapper, i, 0);
+    }
+  }
+
+  return wrapper->fields;
+}
+
 /*
  * for small results, this won't hit the network, but there's no
  * reliable way for us to tell this so we'll always release the GVL
@@ -519,37 +575,16 @@ static VALUE rb_mysql_result_fetch_row(int argc, VALUE * argv, VALUE self) {
     return Qnil;
   }
 
-  if (wrapper->numberOfFields == 0) {
+  rowHash = rb_hash_new();
+  fields = mysql_fetch_fields(wrapper->result);
+  fieldLengths = mysql_fetch_lengths(wrapper->result);
+  if (wrapper->fields == Qnil) {
     wrapper->numberOfFields = mysql_num_fields(wrapper->result);
     wrapper->fields = rb_ary_new2(wrapper->numberOfFields);
   }
 
-  rowHash = rb_hash_new();
-  fields = mysql_fetch_fields(wrapper->result);
-  fieldLengths = mysql_fetch_lengths(wrapper->result);
   for (i = 0; i < wrapper->numberOfFields; i++) {
-
-    // lazily create fields, but only once
-    // we'll use cached versions from here on out
-    VALUE field = rb_ary_entry(wrapper->fields, i);
-    if (field == Qnil) {
-      if (symbolizeKeys) {
-        char buf[fields[i].name_length+1];
-        memcpy(buf, fields[i].name, fields[i].name_length);
-        buf[fields[i].name_length] = 0;
-        field = ID2SYM(rb_intern(buf));
-      } else {
-        field = rb_str_new(fields[i].name, fields[i].name_length);
-#ifdef HAVE_RUBY_ENCODING_H
-        rb_enc_associate(field, utf8Encoding);
-        if (default_internal_enc) {
-          field = rb_str_export_to_enc(field, default_internal_enc);
-        }
-#endif
-      }
-      rb_ary_store(wrapper->fields, i, field);
-    }
-
+    VALUE field = rb_mysql_result_fetch_field(wrapper, i, symbolizeKeys);
     if (row[i]) {
       VALUE val;
       switch(fields[i].type) {
@@ -747,6 +782,7 @@ void Init_mysql2_ext() {
 
   cMysql2Result = rb_define_class_under(mMysql2, "Result", rb_cObject);
   rb_define_method(cMysql2Result, "each", rb_mysql_result_each, -1);
+  rb_define_method(cMysql2Result, "fields", rb_mysql_result_fetch_fields, 0);
 
   VALUE mEnumerable = rb_const_get(rb_cObject, rb_intern("Enumerable"));
   rb_include_module(cMysql2Result, mEnumerable);

ext/mysql2_ext.h

@@ -55,10 +55,10 @@ static void rb_mysql_client_free(void * client);
 typedef struct {
     VALUE fields;
     VALUE rows;
-    unsigned long numberOfFields;
+    unsigned int numberOfFields;
     unsigned long numberOfRows;
     unsigned long lastRowProcessed;
-    int resultFreed;
+    short int resultFreed;
     MYSQL_RES *result;
 } mysql2_result_wrapper;
 #define GetMysql2Result(obj, sval) (sval = (mysql2_result_wrapper*)DATA_PTR(obj));

spec/mysql2/result_spec.rb

@@ -47,6 +47,22 @@ describe Mysql2::Result do
     end
   end
 
+  context "#fields" do
+    before(:all) do
+      @client.query "USE test"
+      @test_result = @client.query("SELECT * FROM mysql2_test ORDER BY id DESC LIMIT 1")
+    end
+
+    it "method should exist" do
+      @test_result.should respond_to(:fields)
+    end
+
+    it "should return an array of field names in proper order" do
+      result = @client.query "SELECT 'a', 'b', 'c'"
+      result.fields.should eql(['a', 'b', 'c'])
+    end
+  end
+
   context "row data type mapping" do
     before(:all) do
       @client.query "USE test"