Conditional Where clause in LINQ

Question

suppose i am showing data in grid and i have many textboxes for filter the data. textbox for employee id. if employee id textbox is empty then no where clause will be added

Answer 1

If you want to mix And operator and Or operator together, check PredicateBuilder out here: http://www.albahari.com/nutshell/predicatebuilder.aspx

You can simply write like:

// begin with true if you start with And operator.
var predicate = PredicateBuilder.True();
predicate = predicate.And(t => t.CureDate < DateTime.UtcNow.AddDays(-1));
// you can mix with Or operator too.
predicate = predicate.Or(t => t.Name.Contains("blah"));

var results = context.TblFamilie
.Where(predicate)
.Select(new
{
  // your projection here...
});


// begin with false if you start with Or operator.
var predicate2 = PredicateBuilder.False();
predicate2 = predicate2.Or(t => t.CureDate < DateTime.UtcNow.AddDays(-1));
// you can mix with And operator too.
predicate2 = predicate2.And(t => t.Name.Contains("blah"));

var results = context.TblFamilie
.Where(predicate)
.Select(new
{
  // your projection here...
});


// even nesting is possible
var inner = PredicateBuilder.False();
inner = inner.Or (p => p.Name.Contains("foo"));
inner = inner.Or (p => p.Name.Contains("bar"));

var outer = PredicateBuilder.True();
outer = outer.And (p => p.CureDate > DateTime.UtcNow.AddDays(-3));
outer = outer.And (p => p.CureDate < DateTime.UtcNow.AddDays(-1));
outer = outer.And (inner);

var results = context.TblFamilie
.Where(outer)
.Select(new
{
  // your projection here...
});

Updated

Okay, lets assume you have a Family class, and you get 'Families' from some where. You can use PredicateBuilder like this:

// you have 4 families from DB, API or anywhere.
var failies = new List
{
    new Family { Id = 1, ParentId = 1, Name = "foo", Birthday = new DateTime(1971, 1, 1) },
    new Family { Id = 1, ParentId = 1, Name = "bar", Birthday = new DateTime(1982, 1, 1) },
    new Family { Id = 1, ParentId = 1, Name = "foobar", Birthday = new DateTime(1993, 1, 1) },
    new Family { Id = 1, ParentId = 1, Name = "fake", Birthday = new DateTime(2000, 1, 1) },
};

// make predicate!
// if a family's Birthday is before than 1980 'or' Name contains "ke".
var predicate = PredicateBuilder.True();
predicate = predicate.And(o => o.Birthday < new DateTime(1980, 1, 1));
predicate = predicate.Or(o => o.Name.Contains("ke"));

// you should make IQueryable in order to use PredicateBuilder.
var result = failies.AsQueryable()
    .Where(predicate)
    .Select(o => new
    {
        o.Id, o.Name, o.Birthday    // only project what you want.
    })
    .ToList();

// now, result should contains "foo" and "fake".
foreach (var family in result)
{
    Debug.WriteLine("Name: " + family.Name);
}

Updated2

You can copy & paste to LinqPad in order to test how it works. Before you run this in the LinqPad,

• Download LinqKit.dll from above link.
• Make sure press 'F4' > Add > Browse > select LinqKit.dll > Add LinqKit namespace in the 'Additional Namespace Imports' tab.
• In the Query panel, choose Language to 'C# Statement(s)'

paste this and run.

// you have 4 strings from DB, API or anywhere.
var strings = new List
{
    "foo",
    "bar",
    "foobar",
    "fake"
};


// make predicate!
// if a string contains "oo" or "ke"
var predicate = PredicateBuilder.True();
predicate = predicate.And(o => o.Contains("oo"));
predicate = predicate.Or(o => o.Contains("ke"));

// you should make IQueryable in order to use PredicateBuilder.
var result = strings.AsQueryable()
    .Where(predicate)
    .ToList();

// now, result should contains "foo", "foobar" and "fake".
foreach (var stringResult in result)
{
    Debug.WriteLine("Name: " + stringResult);
}