Add README files to all examples and fix minor typo bugs

All the README files for all examples have been updated.
Some minor bugs have been fixed in sqlalchemy_examples.

README.md

+# Object-Relational Mapping Examples
+
+In this repository are available some easy Object-Relational Mapping (ORM) examples.
+
+For more details, please refer to the _Lecture 6 – Data Model Implementation_ of the _Open Data Management & the Cloud_ course.

django_example/README.md

+# Django Example
+
+Create the anaconda environment for this example
+
+    conda create -n insurance django
+
+To activate this environment, use
+
+    conda activate insurance
+
+Additional packages are needed, not available in Anaconda but installed with the `pip` command
+
+    pip install django-extensions djangorestframework
+    pip install django-composite-field django-url-filter
+    pip install django-phonenumber-field phonenumbers
+    pip install Pillow
+
+To deactivate an active environment, use
+
+    conda deactivate
+
+## Create a Django Project
+
+Run the following commands
+
+    django-admin startproject insurance
+    cd insurance
+    python manage.py startapp insurancedb
+
+which create a project folder, named insurance, with additional files and then an application, named insurancedb, inside the project.
+It automatically creates skeleton files needed by a Django project and application.
+
+Copy the `admin.py` and `models.py` files to the `insurancedb` folder
+
+    cp ../admin.py insurancedb/
+    cp ../models.py insurancedb/
+
+and copy the `urls.py` and `views.py` file to the `insurance` folder
+
+    cp ../urls.py insurance/
+    cp ../views.py insurance/
+
+Edit the `insurance/setting.py` file adding in the `INSTALLED_APPS` list
+two more elements: `django_extensions` and `insurancedb`. Then your
+application definition should appear like this
+
+    INSTALLED_APPS = [
+        'django.contrib.admin',
+        'django.contrib.auth',
+        'django.contrib.contenttypes',
+        'django.contrib.sessions',
+        'django.contrib.messages',
+        'django.contrib.staticfiles',
+        'django_extensions',
+        'insurancedb',
+    ]
+
+Finally, generate a migration and migrate
+
+    python manage.py makemigrations
+    python manage.py migrate
+
+Insert some data
+
+    python manage.py shell < ../insert.py
+
+Create an admin user
+
+    python manage.py createsuperuser
+
+Run the Django web server
+
+    python manage.py runserver
+
+Access to <http://127.0.0.1:8000>.

euclid_example/README.md

 # ORM Example - Euclid
 
-    git clone https://www.ict.inaf.it/gitlab/odmc/orm_example.git
-    cd orm_example/euclid_example
+Create the anaconda environment for this example
 
-Crea l'ambiente di anaconda
+    conda create -n euclid_example django
+
+To activate this environment, use
 
-    conda create -n euclid_example
     conda activate euclid_example
-    pip install django-extensions djangorestframework django-composite-field django-url-filter
 
-python manage.py migrate
+Additional packages are needed, not available in Anaconda but installed with the `pip` command
+
+    pip install django-extensions djangorestframework
+    pip install django-composite-field django-url-filter
+
+To deactivate an active environment, use
+
+    conda deactivate
+
 
-python manage.py shell
+## Run the Django Project
 
-python manage.py runserver
+Apply migrations
 
-add admin password
+    python manage.py migrate
 
+Create an admin user
 
-## Start from scratch
+    python manage.py createsuperuser
 
-    django-admin startproject euclid_example
-    cd euclid_example
-    python manage.py startapp imagedb
+You can access the database throught the Django shell
 
-Also in settings.py you have to add the name of the app imagedb
+    python manage.py shell
 
-In the imagedb/models.py add the data model classes
+or running the Django web server
 
-Once we have defined our data model in imagedb/models.py we need Django to create the corresponding DB schema
+    python manage.py runserver
 
-python manage.py makemigrations
+then access to <http://127.0.0.1:8000/admin>.

sqlalchemy_example/README.md

+# SQLAlchmy Examples
 
 Create the anaconda environment for this set of examples
 
     conda create -n orm_sqlalchemy sqlalchemy
 
-## # To activate this environment, use
-#
-#     $ conda activate orm_sqlalchemy
-#
-# To deactivate an active environment, use
-#
-#     $ conda deactivate
+To activate this environment, use
 
+    conda activate orm_sqlalchemy
 
+To deactivate an active environment, use
+
+    conda deactivate
+
+
+## Example 1
+
+In this first example we are going to map a single _Car_ table.
+Each _Car_ has an integer _id_ as primary key, a _name_ and a _price_.
+
+Enter the `example_1` directory
+
+    cd example_1
+
+All the SQLAlchmy components
+(engine, declarative base class, mapping and session class)
+are configured in the `mapping.py` file.
+
+Create the database
+
+    python create.py
+
+the SQLite file `example_1.db` has been created.
+Now insert some data
+
+    python insert.py
+
+Select all data in the database
+
+    python read.py
+
+and perform some queries filtered by car name, by id or by car price
+
+    python filter.py
+
+Exit from the example_1 directory
+
+    cd ..
+
+
+## Example 2
+
+In this second example we are going to map two tables, _Author_ and _Book_,
+connected with a one-to-many relation.
+Each _Author_ has an integer _id_ as primary key and a _name_.
+Eack _Book_ has an integer _id_ as primary key, a _title_ and an *author_id* as foreign key.
+
+Enter the `example_2` directory
+
+    cd example_2
+
+All the SQLAlchmy components
+(engine, declarative base class, mapping, relationship and session class)
+are configured in the `mapping.py` file.
+
+Create the database
+
+    python create.py
+
+the SQLite file `example_2.db` has been created.
+Now insert some data
+
+    python insert.py
+
+Perform some queries selecting all books by an author or a book to get its author
+
+    python filter.py
+
+Exit from the example_2 directory
+
+    cd ..
+
+**WARNING**
+In SQLite you have to enable foreign key constraint executing
+
+    PRAGMA foreign_keys=ON;
+
+
+## Example 3
+
+In this third example we are going to map inheritance with three tables, _Client_, _Person_ and _Company_, where a _Client_ can be a _Person_ or a _Company_.
+
+Each _Client_ has an integer _id_ as primary key, an _address_ and a _type_.
+Each _Person_ has an integer _id_ as primary foreign key, a _name_ and a _surname_.
+Each _Company_ has an integer _id_ as primary foreign key, a _company_name_ and a _industry_.
+
+The _type_ discriminates if the _Client_ is also a _Person_ or a _Company_. The _id_ is unique among _Client_, _Person_ and _Company_.
+
+Enter the `example_3` directory
+
+    cd example_3
+
+All the SQLAlchmy components
+(engine, declarative base class, mapping, relationship and session class)
+are configured in the `mapping.py` file.
+
+Create the database
+
+    python create.py
+
+the SQLite file `example_3.db` has been created.
+Now insert some data
+
+    python insert.py
+
+Perform some queries selecting all clients by address or only clients which are persons by address
+
+    python filter.py
+
+Exit from the example_3 directory
+
+    cd ..

sqlalchemy_example/example_2/mapping.py

@@ -28,7 +28,7 @@ class Book(Base):
 
     id = Column(Integer, primary_key=True)
     title = Column(String)      
-    author_id = Column(Integer, ForeignKey("Author.id"))
+    author_id = Column(Integer, ForeignKey("author.id"))
 
     author = relationship("Author")
 

sqlalchemy_example/example_3/filter.py

@@ -25,11 +25,7 @@ results = session.query(Person).filter(Person.address=='via Flavia')
 # Print results
 print('Persons in via Flavia are:')
 for client in results:
-    if client.type == 'person':
-    	print(client.id, client.name, client.surname)
-    elif client.type == 'company':
-    	print(client.id, client.company_name, client.industry)
-
+   	print(client.id, client.name, client.surname)
 
 # Close session
 session.close()