Add error handling

app/corpora/views.py

 from flask import (abort, current_app, flash, redirect, request,
-                   render_template, url_for, send_from_directory)
+                   render_template, session, url_for, send_from_directory)
 from flask_login import current_user, login_required
+from werkzeug import MultiDict
+from werkzeug.utils import secure_filename
 from . import corpora
 from .forms import (AddCorpusFileForm, AddCorpusForm, QueryDownloadForm,
                     QueryForm)
 from .. import db
 from ..models import Corpus, CorpusFile
-from werkzeug.utils import secure_filename
 import os
 import threading
 import logging
@@ -17,32 +18,38 @@ import logging
 def add_corpus():
     add_corpus_form = AddCorpusForm()
     if not add_corpus_form.validate_on_submit():
-        abort(400)
-    corpus = Corpus(creator=current_user,
-                    description=add_corpus_form.description.data,
-                    title=add_corpus_form.title.data)
-    db.session.add(corpus)
-    db.session.commit()
-    dir = os.path.join(current_app.config['OPAQUE_STORAGE_DIRECTORY'],
-                       str(corpus.user_id), 'corpora', str(corpus.id))
-    try:
-        os.makedirs(dir)
-    except OSError:
-        flash('OSError!')
-        db.session.remove(corpus)
+        corpus = Corpus(creator=current_user,
+                        description=add_corpus_form.description.data,
+                        title=add_corpus_form.title.data)
+        db.session.add(corpus)
         db.session.commit()
-    flash('Corpus created!')
-    return redirect(url_for('corpora.corpus', corpus_id=corpus.id))
+        dir = os.path.join(current_app.config['OPAQUE_STORAGE_DIRECTORY'],
+                           str(corpus.user_id), 'corpora', str(corpus.id))
+        try:
+            os.makedirs(dir)
+        except OSError:
+            flash('OSError!')
+            db.session.remove(corpus)
+            db.session.commit()
+        flash('Corpus created!')
+        return redirect(url_for('corpora.corpus', corpus_id=corpus.id))
 
 
 @corpora.route('/<int:corpus_id>')
 @login_required
 def corpus(corpus_id):
+    add_corpus_file_form_data = session.pop('add_corpus_file_form_data',
+                                            default=None)
+    add_corpus_file_form = AddCorpusFileForm(
+        MultiDict(add_corpus_file_form_data)
+    )
+    if add_corpus_file_form_data is not None:
+        add_corpus_file_form.validate()
     corpus = Corpus.query.get_or_404(corpus_id)
     if not (corpus.creator == current_user or current_user.is_administrator()):
         abort(403)
     return render_template('corpora/corpus.html.j2',
-                           add_corpus_file_form=AddCorpusFileForm(),
+                           add_corpus_file_form=add_corpus_file_form,
                            corpus=corpus, title='Corpus')
 
 
@@ -96,27 +103,28 @@ def add_corpus_file(corpus_id):
     if not (corpus.creator == current_user or current_user.is_administrator()):
         abort(403)
     add_corpus_file_form = AddCorpusFileForm()
-    if not add_corpus_file_form.validate_on_submit():
-        abort(400)
-    file = add_corpus_file_form.file.data
-    filename = secure_filename(file.filename)
-    for corpus_file in corpus.files:
-        if filename == corpus_file.filename:
-            flash('File already registered to this corpus.')
-            return redirect(url_for('corpora.corpus', corpus_id=corpus_id))
-    # Save the file
-    dir = os.path.join(str(corpus.user_id), 'corpora', str(corpus.id))
-    file.save(os.path.join(current_app.config['OPAQUE_STORAGE_DIRECTORY'], dir,
-                           filename))
-    author = add_corpus_file_form.author.data
-    publishing_year = add_corpus_file_form.publishing_year.data
-    title = add_corpus_file_form.title.data
-    corpus_file = CorpusFile(author=author, corpus=corpus, dir=dir,
-                             filename=filename,
-                             publishing_year=publishing_year, title=title)
-    db.session.add(corpus_file)
-    db.session.commit()
-    flash('Corpus file added!')
+    if add_corpus_file_form.validate_on_submit():
+        file = add_corpus_file_form.file.data
+        filename = secure_filename(file.filename)
+        for corpus_file in corpus.files:
+            if filename == corpus_file.filename:
+                flash('File already registered to this corpus.')
+                return redirect(url_for('corpora.corpus', corpus_id=corpus_id))
+        # Save the file
+        dir = os.path.join(str(corpus.user_id), 'corpora', str(corpus.id))
+        file.save(os.path.join(current_app.config['OPAQUE_STORAGE_DIRECTORY'],
+                                dir, filename))
+        author = add_corpus_file_form.author.data
+        publishing_year = add_corpus_file_form.publishing_year.data
+        title = add_corpus_file_form.title.data
+        corpus_file = CorpusFile(author=author, corpus=corpus, dir=dir,
+                                 filename=filename,
+                                 publishing_year=publishing_year, title=title)
+        db.session.add(corpus_file)
+        db.session.commit()
+        flash('Corpus file added!')
+    else:
+        session['add_corpus_file_form_data'] = request.form
     return redirect(url_for('corpora.corpus', corpus_id=corpus_id))