From: Albert Schlef <albertschlef@...>
Date: 2009-01-23T00:34:10+09:00
Subject: Re: How to use the type in the Mysql::Field object?

Patrick Put wrote:
> I'm trying to do something like this (not really, I want to use the type
> info instead of just displaying it...):
> 
> fields = $db.list_fields(tablename).fetch_fields
> fields.each do |field|
>   puts "Type = #{field.type} (#{field.type.class})"
> end
> 
> Result:
> Type = 1 (Fixnum)
> Type = 253 (Fixnum)
> Type = 2 (Fixnum)
> Type = 254 (Fixnum)

These constants are defined in some MySQL header file (And perhaps 
MySQL's manual lists their numerical values in its C API section, I 
don't know). That Ruby extension you're using exports them as Ruby 
constants as well; e.g. Mysql::Field::TYPE_SHORT, 
Mysql::Field::TYPE_FLOAT, etc.

Note that there are numerous Mysql Ruby extensions: DBI's, DataMapper's, 
ActiveRecord's.

If you look at do_mysql's 'do_mysql_ext.c' (That's DataObjects's, which 
is DataMapper's), you'll find a useful infer_ruby_type() with a big case 
statemnt. Here it is:

// Figures out what we should cast a given mysql field type to
static VALUE infer_ruby_type(MYSQL_FIELD *field) {

  char* ruby_type;

  switch(field->type) {
    case MYSQL_TYPE_NULL: {
      ruby_type = NULL;
      break;
    }
    case MYSQL_TYPE_TINY: {
      ruby_type = "TrueClass";
      break;
    }
    case MYSQL_TYPE_BIT:
    case MYSQL_TYPE_SHORT:
    case MYSQL_TYPE_LONG:
    case MYSQL_TYPE_INT24:
    case MYSQL_TYPE_LONGLONG:
    case MYSQL_TYPE_YEAR: {
      ruby_type = "Fixnum";
      break;
    }
    case MYSQL_TYPE_DECIMAL:
    case MYSQL_TYPE_NEWDECIMAL: {
      ruby_type = "BigDecimal";
      break;
    }
    case MYSQL_TYPE_FLOAT:
    case MYSQL_TYPE_DOUBLE: {
      ruby_type = "Float";
      break;
    }
    case MYSQL_TYPE_TIMESTAMP:
    case MYSQL_TYPE_DATETIME: {
      ruby_type = "DateTime";
      break;
    }
    case MYSQL_TYPE_TIME: {
      ruby_type = "DateTime";
      break;
    }
    case MYSQL_TYPE_DATE:
    case MYSQL_TYPE_NEWDATE: {
      ruby_type = "Date";
      break;
    }
    default: {
      ruby_type = "String";
      break;
    }
  }

  return rb_str_new2(ruby_type);
}

Maybe your extension has a similar funcion. Look in its .c file. E.g., 
search for "_TYPE_DOUBLE" to arrive at the relevant places.

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