Object-relational impedance mismatch refers to the challenges that arise when you try to bridge the differences between object-oriented programming languages (which use object models) and relational databases. Here’s a breakdown of why this happens:

1. Data Structure Mismatch:
   • Object Model: Organizes data in objects and classes, using attributes and methods that represent real-world entities. Objects may contain nested objects, hierarchies, and complex relationships.
   • Relational Database: Organizes data in tables with rows and columns, following strict schemas. Relationships between entities are represented through foreign keys and join tables.

This structural difference makes it difficult to directly map objects to tables.

1. Inheritance:

   • Object Model: Allows for inheritance, meaning that a class can inherit properties and behavior from another class.
   • Relational Database: Lacks a straightforward way to represent inheritance. This typically requires extra tables or additional columns in relational models to mimic inheritance, complicating data design and retrieval.

2. Identity and References:

   • Object Model: Uses direct object references, meaning an object has a pointer to another object, forming a web of interconnected instances.
   • Relational Database: Uses foreign keys and joins to establish relationships, which requires querying and joining tables to retrieve related data.

3. Data Retrieval:

   • Object Model: Can directly access related objects (e.g., user.address.street).
   • Relational Database: Requires SQL queries, often involving multiple joins, which can lead to complex query logic.

4. CRUD Operations:

   • Object Model: Can be less predictable when saved to a relational database due to cascades of complex relationships and updates, making transactional control challenging.
   • Relational Database: Designed to handle CRUD operations but with simpler data models. Object-oriented models need ORMs (Object-Relational Mappers) to translate objects to tables and vice versa.

Solutions to Impedance Mismatch

ORM (Object-Relational Mapping) frameworks like Hibernate (Java), SQLAlchemy (Python), and Entity Framework (.NET) help map objects to relational tables, providing an abstraction that simplifies CRUD operations.