where-clause.md

Filtering with Where

The where clause is used to apply filter predicates to your query. It supports a very wide variety of operators and methods when translating to N1QL.

Basic Usage

To apply a where clause, simply add it to the LINQ query along with an expression that returns a Boolean result.

var context = new BucketContext(bucket);

var query = from beer in context.Query<Beer>()
            where beer.Abv == 6
            select beer;

await foreach (var doc in query.AsAsyncEnumerable()) {
    // do work
}

The above example will return all beers with an ABV of exactly 6.

Compound Expressions

The where clause supports Boolean operations (&& and ||) to combine multiple predicates.

var context = new BucketContext(bucket);

var query = from beer in context.Query<Beer>()
            where (beer.Abv == 6) && (beer.Name != null)
            select beer;

await foreach (var doc in query.AsAsyncEnumerable()) {
    // do work
}

It is also valid to extend the query with multiple where clauses.

var context = new BucketContext(bucket);

var query = from beer in context.Query<Beer>()
            where.beer.Abv == 6
            select beer;

if (nameRequired) { // local variable
    query = from beer in query
            where beer.Name != null
            select beer;
}

await foreach (var doc in query.AsAsyncEnumerable()) {
    // do work
}

Document Type Filters

Some where clauses may be automatically applied to your query based on the document type you are querying. For example, it is common to use DocumentTypeFilter attributes on your document objects so they are automatically limited to documents with a certain "type" attribute. For more information, see Mapping JSON documents to POCOs with DocumentFilters.

Supported Operators

The following operators are supported by Linq2Couchbase.

• Equality (==)
• Inequality (!=)
• Greater Than (>)
• Less Than (<)
• Greater Than Or Equal (>=)
• Less Than Or Equal (<=)
• Boolean And (&&)
• Boolean Or (||)
• Boolean Not (!)
• Addition (+)
• Subtraction/Negation (-)
• Multiplication (*)
• Division (/)
• Modulus (%)
• Coalesce (??)
• Conditional Expressions (a ? b : c)