Adding a String of a filename or absolute path to a database when using Flask-Admin and SQLAlchemy - flask

Question

I am working with SQLAlchemy and Flask-Admin right now. Let us say that I am trying to get a String of the file name or a String of the absolute path of the file name of an image file. I am trying to insert either of these into a database automatically when I create a user. The code that I am using is structured similar to this.  
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
url_pic = Column(String(50), nullable=False)
pic = Column(LargeBinary, nullable=False)
...
from flask.ext.admin.contrib.sqla import ModelView
from flask.ext.admin.form.upload import FileUploadField
from wtforms.validators import ValidationError
from flask.ext.admin import Admin
from flask.ext.sqlalchemy import SQLAlchemy
from flask import Flask
import imghdr
app = Flask(__name__)
db = SQLAlchemy(app)
class UserAdminView(ModelView):
def picture_validation(form, field):
if field.data:
filename = field.data.filename
if filename[-4:] != '.jpg':
raise ValidationError('file must be .jpg')
if imghdr.what(field.data) != 'jpeg':
raise ValidationError('file must be a valid jpeg image.')
field.data = field.data.stream.read()
return True
form_columns = ['id','url_pic', 'pic']
column_labels = dict(id='ID', url_pic="Picture's URL", pic='Picture')
def pic_formatter(view, context, model, name):
return 'NULL' if len(getattr(model, name)) == 0 else 'a picture'
column_formatters = dict(pic=pic_formatter)
form_overrides = dict(pic= FileUploadField)
form_args = dict(pic=dict(validators=[picture_validation]))
admin = Admin(app)
admin.add_view(UserAdminView(User, db.session, category='Database Administration'))
...
How could we get a string version of the file name or absolute path when using the picture_validation function? Right now, the function only provides the binary data of the file, which isn’t as useful.