added in loans support, also particular route for book_for_loan without markup used as div content on loan.html page via ajax load

loan.py

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+from wtforms import SubmitField, StringField, HiddenField, validators, TextAreaField
+from flask_wtf import FlaskForm
+from flask import request, render_template
+from wtforms.fields.html5 import DateField
+from __main__ import db, app, ma
+
+################################################################################
+# Class describing Loan in the database, and via sqlalchemy, connected to the DB as well
+################################################################################
+class Loan(db.Model):
+    id = db.Column(db.Integer, unique=True, nullable=False, primary_key=True)
+    surname = db.Column(db.String(30), unique=False, nullable=False)
+    firstnames = db.Column(db.String(50), unique=False, nullable=False)
+    contact_details = db.Column(db.String(256), unique=False, nullable=False)
+    date_lent = db.Column(db.Date, nullable=False )
+
+    def __repr__(self):
+        return "<id: {}, firstnames: {}, surname: {}>".format(self.id,self.firstnames, self.surname)
+
+################################################################################
+# Helper class that inherits a .dump() method to turn class Loan into json / useful in jinja2
+################################################################################
+class LoanSchema(ma.SQLAlchemyAutoSchema):
+    class Meta:
+        model = Loan
+        ordered = True
+
+################################################################################
+# Helper class that defines a form for loan, used to make html <form>, with field validation (via wtforms)
+################################################################################
+class LoanForm(FlaskForm):
+    id = HiddenField()
+    firstnames = StringField('FirstName(s):', [validators.DataRequired()])
+    surname = StringField('Surname:', [validators.DataRequired()])
+    contact_details = TextAreaField('Contact Details:', [validators.DataRequired()])
+    surname = StringField('Surname:', [validators.DataRequired()])
+    date_lent = DateField('Date Lent:', format='%Y-%m-%d' )
+    submit = SubmitField('Save' )
+    delete = SubmitField('Delete' )
+
+################################################################################
+# Routes for loan data
+#
+# /loans -> GET only -> prints out list of all loans
+################################################################################
+@app.route("/loans", methods=["GET"])
+def loans():
+    loans = Loan.query.all()
+    return render_template("loans.html", loans=loans)
+
+################################################################################
+# /loan/<id> -> GET/POST(save or delete) -> shows/edits/delets a single loan
+################################################################################
+@app.route("/loan/<id>", methods=["GET", "POST"])
+def loan(id):
+    ### DDP: should this be request.form or request.values?
+    alert="Success"
+    loan_form = LoanForm(request.form)
+    if request.method == 'POST' and loan_form.validate_on_submit():
+        id = request.form['id']
+        loan = Loan.query.get(id)
+        try:
+            request.form['submit']
+        except:
+            message="Sorry, Deleting unsupported at present"
+            alert="Danger"
+        else:
+            loan.firstnames = request.form['firstnames']
+            loan.surname = request.form['surname']
+            loan.surname = request.form['surname']
+            loan.contact_details = request.form['contact_details']
+            loan.date_lent = request.form['date_lent']
+            db.session.commit()
+            message="Successfully Updated Loan (id={})".format(id)
+    else:
+        loan = Loan.query.get(id)
+        loan_form = LoanForm(request.values, obj=loan)
+        message=""
+    return render_template("loan.html", loan=loan, alert=alert, message=message, loan_form=loan_form)

templates/books_for_loan.html

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+	<h3>Loaned Books</h1>
+	<table id="book_table" class="table table-striped table-sm" data-toolbar="#toolbar" data-search="true">
+	  <thead>
+	  <tr class="thead-light"><th>Title</th></tr>
+	  </thead>
+	  <tbody>
+      {% for book in books %}
+        <tr>
+		  {% if book.sub_book_num is defined %}
+		  	<td data-sort="{{book.parent_id}}.{{book.sub_book_num}}"><a href="/book/{{book.id}}">&nbsp;&nbsp;&nbsp;&nbsp;{{book.title}}</a></td>
+		  {% else %}
+		  	<td data-sort="{{book.id}}"><a href="/book/{{book.id}}">{{book.title}}</a></td>
+		  {% endif %}
+		</tr>
+      {% endfor %}
+	</tbody>
+	</table>

templates/loan.html

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+{% extends "base.html" %}
+{% block main_content %}
+	<div class="container">
+		<h3 class="col-lg-12"><center>Loan</center></h3>
+		{% if message|length %}
+			<div class="row alert alert-{{alert}}">
+			{{message}}
+			</div>
+		{% endif %}
+		<div class="row">
+			<div class="col-lg-8">
+			<form class="form form-inline col-lg-12" action="" method="POST">
+				{{ loan_form.csrf_token }}
+				{{ loan_form.id }}
+				<div class="form-row col-lg-12">
+				{{ loan_form.firstnames.label( class="col-lg-2" ) }}
+				{{ loan_form.firstnames( class="form-control col-lg-10" ) }}
+				</div class="form-row">
+				<div class="form-row col-lg-12">
+				{{ loan_form.surname.label( class="col-lg-2" ) }}
+				{{ loan_form.surname( class="form-control col-lg-10" ) }}
+				</div class="form-row">
+				<div class="form-row col-lg-12">
+				{{ loan_form.date_lent.label( class="col-lg-2" ) }}
+				{{ loan_form.date_lent( class="form-control col-lg-10" ) }}
+				</div class="form-row">
+				<div class="form-row col-lg-12">
+				{{ loan_form.contact_details.label( class="col-lg-2" ) }}
+				{{ loan_form.contact_details( class="form-control col-lg-10", rows="5" ) }}
+				</div class="form-row">
+				<div class="row col-lg-12">
+				<br>
+				</div class="row">
+				<div class="form-row col-lg-12">
+					{{ loan_form.delete( class="btn btn-outline-danger col-lg-2" )}}
+					{{ loan_form.submit( class="btn btn-primary col-lg-2" )}}
+				</div class="form-row">
+			</form>
+			</div class="col-lg-8">
+			<div class="col-lg-4">
+				<div id="books_for_loan_bit">
+				</div id="books_for_loan_bit">
+			</div class="col-lg-4">
+		</div class="row">
+	</div class="container">
+{% endblock main_content %}
+{% block script_content %}
+	<script>
+		$(document).ready( function() {
+			$("#books_for_loan_bit").load("/books_for_loan/" + {{loan_form.data.id}})
+		} )
+	</script>
+{% endblock script_content %}

templates/loans.html

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+{% extends "base.html" %}
+
+{% block main_content %}
+<h3>Loans</h3>
+<table id="book_table" class="table table-striped table-sm" data-toolbar="#toolbar" data-search="true">
+	<thead>
+		<tr class="thead-light"><th>Surname</th><th>Firstname(s)</th><th>Date Lent</th><th>Contact Details</th></tr>
+	</thead>
+	<tbody>
+	{% for loan in loans %}
+		<tr><td><a href="{{url_for('loan', id=loan.id )}}">{{loan.surname}}</a></td><td>{{loan.firstnames}}</td><td>{{loan.date_lent}}</td>
+		<td>{{loan.contact_details}}</td></tr>
+	{% endfor %}
+	</tbody>
+</table>
+{% endblock main_content %}