Gracefully catch IntegrityError when a database constraint is violated

webapi.py

@@ -10,6 +10,7 @@ from flask import Flask, jsonify, request
 from flask_api import status
 
 from sqlalchemy.orm.exc import NoResultFound
+from sqlalchemy.exc import IntegrityError
 from libdb import Session, Location, ProductQuantity, Product, Brand, Unit, Purchase, Use
 
 
@@ -258,10 +259,13 @@ def api_create_location():
     newlocation = Location(name=locname, description=locdesc)
     session.add(newlocation)
     print("added newlocation")
+    try:
         session.commit()
         print("committed")
-
         return jsonify({'api_endpoints': f'/api/v1/location/name/{locname}'})
+    except IntegrityError:
+        session.rollback()
+        return jsonify({'error': 'INTEGRITY_ERROR'})
 
 
 @app.route("/api/v1/create_brand", methods=["POST"])
@@ -280,10 +284,13 @@ def api_create_brand():
     newbrand = Brand(name=brandname, description=branddesc)
     session.add(newbrand)
     print("added newbrand")
+    try:
         session.commit()
         print("committed")
-
         return jsonify({'api_endpoints': [f'/api/v1/brand/name/{brandname}']})
+    except IntegrityError:
+        session.rollback()
+        return jsonify({'error': 'INTEGRITY_ERROR'})
 
 
 @app.route("/api/v1/create_product", methods=["POST"])
@@ -305,11 +312,14 @@ def api_create_product():
                          description=desc)
     session.add(newproduct)
     print("added newproduct")
+    try:
         session.commit()
         print("committed")
-
         return jsonify({'api_endpoints': [f'/api/v1/product/upc/{request.form["upc"]}',
                                         f'/api/v1/product/name/{request.form["name"]}']})
+    except IntegrityError:
+        session.rollback()
+        return jsonify({'error': 'INTEGRITY_ERROR'})
 
 
 @app.route("/api/v1/create_unit", methods=["POST"])
@@ -328,10 +338,13 @@ def api_create_unit():
     newunit = Unit(name=unitname, description=unitdesc)
     session.add(newunit)
     print("added newunit")
+    try:
         session.commit()
         print("committed")
-
         return jsonify({'api_endpoints': [f'/api/v1/unit/name/{unitname}']})
+    except IntegrityError:
+        session.rollback()
+        return jsonify({'error': 'INTEGRITY_ERROR'})
 
 
 @app.route("/api/v1/create_purchase", methods=["POST"])
@@ -347,10 +360,13 @@ def api_create_purchase():
                            date=request.form['date'], location=request.form['location'])
     session.add(newpurchase)
     print("added newpurchase")
+    try:
         session.commit()
         print("committed")
-
         return jsonify({'api_endpoints': [f'/api/v1/purchase/id/{newpurchase.id}']})
+    except IntegrityError:
+        session.rollback()
+        return jsonify({'error': 'INTEGRITY_ERROR'})
 
 
 @app.route("/api/v1/create_use", methods=["POST"])
@@ -366,10 +382,13 @@ def api_create_use():
                  date=request.form['date'], location=request.form['location'])
     session.add(newuse)
     print("added newuse")
+    try:
         session.commit()
         print("committed")
-
         return jsonify({'api_endpoints': [f'/api/v1/use/id/{newuse.id}']})
+    except IntegrityError:
+        session.rollback()
+        return jsonify({'error': 'INTEGRITY_ERROR'})
 
 
 if __name__ == "__main__":