Linq.Fluent.PredicateBuilder 1.0.1

Linq.Fluent.PredicateBuilder

Fluent Predicate Builder

Basically, you have to provide a predicate to the Linq Where method.

Using the fluent PredicateBuilder, you can perform

• And
• AndAlso
• Or
• OrElse

operations, to build your predicate.

In below example, an item is matched if any of the 3 predicates match.

var list = Enumerable.Range(1, 10000000);

var predicate = new PredicateBuilder<int>()
                        .Initial(x => x >= 12 && x <= 13)
                        .Or(x => x <= 2)
                        .Or(x => x > 99999999)
                .ToPredicate();

var result = list.Where(predicate)
                 .ToList();

Assert.Equal(4, result.Count());

Also, You can create predicates based on conditions.

Eg. In below query, all employees are returned if restrict is false.

Only 1 employee is returned if restrict is true.

[Theory(DisplayName = "Test_Fluent_PredicateBuilder_Conditional")]
[InlineData(true)]
[InlineData(false)]
public void Test_Fluent_PredicateBuilder_Conditional(bool restrict)
{
    var list = new List<Employee>
    {
        new Employee { Id = 1, Name = "Cliff", Department = "Human Resources"},
        new Employee { Id = 2, Name = "John", Department = "IT"}
    };

    var predicate = new PredicateBuilder<Employee>()
                            .Initial(e => true)
                            .And(restrict,  e => e.Department == "IT")
                    .ToPredicate();

    var result = list.Where(predicate)
                        .ToList();

    if (restrict)
    {
        Assert.Single(result);
        Assert.Equal("John", result[0].Name);
    }                
    else
    {
        Assert.Equal(2, result.Count());
        Assert.Equal("Cliff", result[0].Name);
        Assert.Equal("John", result[1].Name);
    }                
}

Note:

ToPredicate produces a predicate (Func<T, bool>).

This can be used with IEnumerable<T>.Where.

ToExpressionPredicate produces an expression predicate (Expression<Func<T, bool>>).

This can be used with IQueryable<T>.Where

Linq Where extensions

There is also an easy to use Linq Where extensions.

Based on operation

Just select the operation and specify the predicates.

All predicates are combined as per the specified operation by the extension.

var list = Enumerable.Range(1, 10000000);

var result = list.Where(Operation.Or,
                            x => x >= 12 && x <= 13,
                            x => x <= 2,
                            x => x > 99999999)
                 .ToList();

Assert.Equal(4, result.Count());

With Predicate Builder

var list = Enumerable.Range(1, 10000000);

var result = list.Where(builder => builder.Initial(x => x >= 12 && x <= 13)
                                          .Or(x => x <= 2)
                                          .Or(x => x > 99999999)
                                    .ToPredicate())
                 .ToList();

Assert.Equal(4, result.Count());

Note:

There are 2 Where extensions each for:

• IEnumerable<T>.Where
• IQueryable<T>.Where