Linqkit PredicateBuilder: And/or Nested Combinations of Predicates

Linqkit PredicateBuilder is a powerful library for building dynamic LINQ expressions. It provides a set of extension methods for building predicates, which are expressions that return a boolean value, for use in querying data.

One of the key features of PredicateBuilder is the ability to create nested combinations of predicates using the And and Or methods. This allows you to build complex search conditions that can be dynamically generated at runtime, based on user input or other parameters.

Basic Usage

The simplest way to use PredicateBuilder is to create a predicate that checks a single condition on a given entity. For example, to find all customers whose name contains the string "Smith," you could write:

var predicate = PredicateBuilder.New<Customer>(c => c.Name.Contains("Smith"));

The predicate can then be used in a LINQ query to retrieve the matching customers:

var customers = dbContext.Customers.Where(predicate);

Combining Predicates with And

To create more complex search conditions, you can use the And method to combine multiple predicates together. For example, to find all customers whose name contains "Smith" and who live in New York, you could write:

var predicate = PredicateBuilder.New<Customer>(c => c.Name.Contains("Smith"))
                  .And(c => c.City == "New York");

The resulting predicate will match only customers who satisfy both conditions.

Combining Predicates with Or

Alternatively, you can use the Or method to create a predicate that matches either of two conditions. For example, to find all customers whose name contains "Smith" or who live in New York, you could write:

var predicate = PredicateBuilder.New<Customer>(c => c.Name.Contains("Smith"))
                  .Or(c => c.City == "New York");

This predicate will match any customer who satisfies either condition.

Nesting Predicates

You can also nest combinations of predicates by using the parentheses operator. For example, to find all customers whose name contains "Smith" and who either live in New York or have a phone number starting with "555," you could write:

var predicate = PredicateBuilder.New<Customer>(c => c.Name.Contains("Smith"))
                  .And(
                      PredicateBuilder.New<Customer>(c => c.City == "New York")
                          .Or(c => c.Phone.StartsWith("555"))
                  );

This predicate will match only customers who satisfy both the "Smith" condition and either the "New York" or "555" condition.

Conclusion

Linqkit PredicateBuilder is a powerful tool for building dynamic search conditions in LINQ. By combining predicates with And, Or, and parentheses, you can create complex queries that can be dynamically generated at runtime.