<h1>Creating OR statements in NHibernate: A comprehensive guide</h1>
<p>NHibernate is a popular object-relational mapping (ORM) tool used in the .NET framework for database access. It allows developers to work with databases using object-oriented programming concepts, making database operations more intuitive and efficient.</p>
<p>One common task in database operations is querying data using logical operators, such as OR statements. In this guide, we will explore how NHibernate handles OR statements and provide a comprehensive guide on how to create them.</p>
<h2>Understanding OR statements</h2>
<p>OR statements are logical operators used in database queries to retrieve data that meets one or more conditions. It allows us to specify multiple conditions and retrieve data that satisfies at least one of those conditions.</p>
<p>For example, let's say we have a database table called "Products" with columns for "product_name," "category," and "price." We want to retrieve all products that are either in the "Electronics" category or have a price higher than $100. This can be achieved using an OR statement.</p>
<h2>Creating OR statements in NHibernate</h2>
<p>NHibernate provides two ways to create OR statements: using the Criteria API or using HQL (Hibernate Query Language).</p>
<h3>Using the Criteria API</h3>
<p>The Criteria API is a programmatic way of creating database queries in NHibernate. It allows us to build queries using fluent syntax and supports various logical operators, including OR statements.</p>
<p>To create an OR statement using the Criteria API, we first need to create a Criteria object for the entity we want to query. In our example, it would be the "Products" entity. Then, we can use the "Add" method to add multiple conditions to our query, separated by the OR operator.</p>
<pre>
<code>var criteria = session.CreateCriteria<Product>();
criteria.Add(Restrictions.Or(
Restrictions.Eq("category", "Electronics"),
Restrictions.Gt("price", 100)
));
</code>
</pre>
<p>The above code will generate a query that retrieves all products that are either in the "Electronics" category or have a price higher than $100.</p>
<h3>Using HQL</h3>
<p>HQL is a powerful query language similar to SQL but designed specifically for NHibernate. It allows us to write database queries in a more readable and concise way compared to the Criteria API.</p>
<p>To create an OR statement using HQL, we can use the "or" keyword followed by the conditions we want to combine, separated by the OR operator.</p>
<pre>
<code>var query = session.CreateQuery("FROM Product p WHERE p.category = 'Electronics' OR p.price > 100");
</code>
</pre>
<p>The above query will retrieve the same results as the one we created using the Criteria API.</p>
<h2>Handling NULL values</h2>
<p>One thing to keep in mind when creating OR statements in NHibernate is how it handles NULL values. When using the Criteria API, if one of the conditions evaluates to NULL, the entire OR statement will evaluate to NULL, and no results will be returned. This behavior is different from SQL, where NULL values are ignored when using logical operators.</p>
