Adding or to linq query

Question

It is possible to add or to linq query after declaration?

I mean if i have :

Query.Where(f => some-condition );

I wand to add "OR" after that:

if (some-condition) 
   Query.WhereOr(f => some-condition );

It's C# code. How do you usually implemtn an OR operator in C#? This is the same: `Where(f => some-condition || some-other-condition)`. Don't try to overcomplicate things. — jmcilhinney, Nov 21 '17 at 07:43
I think, before adding that condition, there was an if statement first? @jmcilhinney — Willy David Jr, Nov 21 '17 at 07:45
If you keep the `Query` around (without `Where` applied) it might be possible to work with something like `Query.Where(cond1).Union(Query.Where(cond2))` but I don't know whether the result will be any similar to a simple `||` — grek40, Nov 21 '17 at 07:46

Drag and Drop · Answer 1 · 2017-11-21T09:40:44.387

Looks like you could be looking for a Predicate builder Or you can just stack some .Where clause as linq is lazy.

As your question lacks of context, imagine querying a Person table based on a form (2 fields/1 checkbox).

// Where Stacking
if (!string.IsNullOrEmpty(FieldA.Text))
{// OR
    result = query.Where(item => item.Something.Contains(FieldA.Text));
}
if (!string.IsNullOrEmpty(FieldB.Text))
{// AND
    result = result.Where(item => item.SomethingElse.Contains(FieldB.Text));
}

// Predicate
if (CheckBox1.Checked || CheckBox2.Checked || CheckBox3.Checked))
{//Here your initialise your predicate to false because you are going to do OR
    var predicate = PredicateBuilder.False<SearchItem>();
    if(CheckBox1.Checked) predicate = predicate.Or(item => item.Foo == 1);
    if(CheckBox2.Checked) predicate = predicate.Or(item => item.Foo == 2);
    if(CheckBox3.Checked) predicate = predicate.Or(item => item.Foo == 3);
    result = result.Where(predicate);
}

Stacking Where is a good solution but can produce a little overheat but nothing that is really noticable.

PS: Article of Jon about nesting where https://codeblog.jonskeet.uk/2011/06/16/linq-to-objects-and-the-performance-of-nested-quot-where-quot-calls/

Wouldn't stacking `.Where` clauses behave as `and` instead of `or` ? — Rafalon, Nov 21 '17 at 09:26
@Rafalon, it's not the stacking that cause AND, OR but the `**query** = **query**.Where` — Drag and Drop, Nov 21 '17 at 09:38
Then what do you mean by stacking ? I tried `integers.Where(x => x > 3).Where(x => x < 5)` where `integers == {1,2,3,4,5,6}` and it returns only 4 as if it was `integers.Where(x => x > 3 && x < 5)` — Rafalon, Nov 21 '17 at 09:40
@Rafalon, I have edit my thought into code. But your are right and this way can behave as a sub query instead of a or close depending on a lot of things. — Drag and Drop, Nov 21 '17 at 09:46

score 0 · Answer 2 · answered Nov 21 '17 at 08:32

0

You should use LinqKit.PredicateBuilder class

Example:

var predicate = PredicateBuilder.True<Product>();
if(inputPrice > 100)
   predicate = predicate.And (p => p.Price > 100);
if(inputName == "S%")
   predicate = predicate.And (p => p.Name.StartsWith("S"));

Finally,

var result = products.Where(predicate);

More details Wiki

answered Nov 21 '17 at 08:32

Sunil

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Shouldn't your example be about `Or` for this question? – grek40 Nov 21 '17 at 08:51

reckface · Answer 3 · 2017-11-21T08:37:26.407

0

IEnumerable and IQueryable to some extent will allow you to chain conditions

Query.Where(f=> some-condition || some_other_condition);
// or
var q = Query.Where(f=> some-condition)
if(stuff_needs_to_happen)
  q = q.Where(f => stuff_that_needs_to_happen)

The reason for the "to some extent" is that with IQueryable the underlying query language may not support some of the conditions in the predicate (custom functions and so on).

edited Nov 21 '17 at 08:37

answered Nov 21 '17 at 08:34

reckface

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I believe the second part is equivalent to `Query.Where(f => some-condition && stuff_that_needs_to_happen)` and not to `Query.Where(f => some-condition || stuff_that_needs_to_happen)` – Rafalon Nov 21 '17 at 09:18

Adding or to linq query

3 Answers3