C# Predicate builder with using AND with OR

问题

I have the following class:

public class testClass
{
    public string name { get; set; }
    public int id { get; set; }
    public int age { get; set; }
}

and the following code:

            var list = new List<testClass>();
            list.Add(new testClass { name = "name", id = 1, age = 30 });
            list.Add(new testClass { name = "name", id = 2, age = 22 });
            list.Add(new testClass { name = "name", id = 3, age = 20 });
            list.Add(new testClass { name = "name", id = 4, age = 30 });
            list.Add(new testClass { name = "name", id = 5, age = 27 });
            list.Add(new testClass { name = "name", id = 6, age = 30 });

            var qble = list.AsQueryable();

            var pred = PredicateBuilder.New<testClass>();
            pred.Or(x => x.name == "name" && x.id == 1);
            pred.Or(x => x.age == 30);
            var predQuery = qble.AsExpandable().Where(pred);

My aim is to create a query that returns all records where:

id = 1 and name = "name"

age = 30

So for the query above, it should return the items at index 0, 1, 5

For the above query it does as I want.

However, I now want to the build the predicate by combining a set of queries, rather than explicitly defining them. So I now have the following 2 queries:

var query1 = list.Where(x => x.name == "name" && x.id == 1);
var query2 = list.Where(x => x.age == 30);

and I want to build the query based on the variables query1 and query2, without explicitly defining the conditions - as these conditions will be dynamically defined and I do not know what they are,and they will be defined in different places.

My guess is I need to do something like this (continuing from above):

var qble = list.AsQueryable();

var query1 = list.Where(x => x.name == "name" && x.id == 1);
var query2 = list.Where(x => x.age == 30);

var pred = PredicateBuilder.New<testClass>();
pred.Or(query1);
pred.Or(query2);
var predQuery = qble.AsExpandable().Where(pred);

but this is not quite correct as the predicate builder will not accept the query as a parameter.

Can this be done?

回答1:

You could create two Predicate<T> and invoke them in your .Where call at the end.

var qble = list.AsQueryable();

var query1 = new Predicate<testClass>(x => x.name == "name" && x.id == 1);
var query2 = new Predicate<testClass>(x => x.age == 30);

var predQuery = qble.AsExpandable().Where(x => query1(x) || query2(x));

Or you could build another Predicate<T> beforehand and use this

var query = new Predicate<testClass>(x => query1(x) || query2(x));
var predQuery = qble.AsExpandable().Where(query);

来源：https://stackoverflow.com/questions/45962131/c-sharp-predicate-builder-with-using-and-with-or

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predicatebuilder