How to combine multiple conditional query in one query for elasticsearch .net client

Question

I'm new to using elastic search. I'm using the .NET client version 8.12 (nuget package: Elastic.Clients.Elasticsearch), I'm trying to send a query based on parameters. Only add the condition if the parameter value exists. Below is the code for the query:

public class ProductSearchDto
{
    public string? Term { get; set; }
    public string? CategoryId { get; set; }
    public int? PriceFrom { get; set; }
    public int? PriceTo { get; set; }
    public int? Stars { get; set; }
    public int Page { get; set; }
    public int PageSize { get; set; }
}

The index class:

public class ProductIndex 
{
    public string Id { get; set; }
    public decimal Price { get; set; }
    public string Title { get; set; }
    public string Description { get; set; }
    public string CategoryId { get; set; }
    public int Stars { get; set; }
    public DateTime IndexedAt { get; set; } = DateTime.UtcNow;
}

Also, for the generation of the query below is the code that calls elastic search:

public async Task<List<ProductIndex>> Search(ProductSearchDto searchDto)
        {
            QueryDescriptor<ProductIndex> query = new QueryDescriptor<ProductIndex>();
            if (!string.IsNullOrEmpty(searchDto.Term))
            {
                 query
                .Match(r => r.Field(y => y.Description).Query(searchDto.Term));
            }
            if (!string.IsNullOrEmpty(searchDto.CategoryId))
            {
                query
               .Match(r => r.Field(y => y.CategoryId).Query(searchDto.CategoryId));
            }
            if (searchDto.Stars.HasValue)
            {
                query
               .Match(r => r.Field(y => y.Stars).Query(searchDto.Stars.Value.ToString()));
            }
            if (searchDto.PriceFrom.HasValue)
            {
                query
               .Range(r => r.NumberRange(z => z.Field(t => t.Price).From(searchDto.PriceFrom)
               .To(searchDto.PriceTo)));
            }
            var result = await _searchOperation.SearchIndexElastic<ProductIndex>
                (query);
            return result;
        }

I debugged the query and it always just sending one parameter although other conditions are still active. Any other ways?

Answer 1

Your initial code tried to sequentially add conditions to a single QueryDescriptor<ProductIndex> instance. That might not work because each call to a method like .Match or .Range on the QueryDescriptor does not add a new condition to an accumulating list of conditions.
Instead, each call configures the descriptor anew, which means only the last configuration applied before the search is executed will take effect. Hence, "it's always just sending one parameter, although other conditions are still active".

---

From Sagar Patel's suggestion, the key to combining multiple conditional queries in a single Elasticsearch query would be to use a Bool query with Must clauses.

But:

Thank you for the suggestion, but I would like to point out that this code is using the NEST package, I'm using the latest package 8.12, and the classes mentioned "QueryContainer" and "QueryContainerDescriptor" are no longer used.

Meaning elastic/elasticsearch-net issue 8002 applies.

Found a workaround to use Query object and not the facades. However it will be nice to port the functionality to the new 8.x API. So try and construct your query using a more direct approach with the Query objects, combining them conditionally based on the existence of your search parameters.

public async Task<List<ProductIndex>> Search(ProductSearchDto searchDto)
{
    var mustQueries = new List<Func<QueryContainerDescriptor<ProductIndex>, QueryContainer>>();

    if (!string.IsNullOrEmpty(searchDto.Term))
    {
        mustQueries.Add(q => q.Match(m => m.Field(f => f.Description).Query(searchDto.Term)));
    }
    if (!string.IsNullOrEmpty(searchDto.CategoryId))
    {
        mustQueries.Add(q => q.Match(m => m.Field(f => f.CategoryId).Query(searchDto.CategoryId)));
    }
    if (searchDto.Stars.HasValue)
    {
        mustQueries.Add(q => q.Term(t => t.Field(f => f.Stars).Value(searchDto.Stars.Value)));
    }
    if (searchDto.PriceFrom.HasValue && searchDto.PriceTo.HasValue)
    {
        mustQueries.Add(q => q.Range(r => r.Field(f => f.Price).GreaterThanOrEquals(searchDto.PriceFrom.Value).LessThanOrEquals(searchDto.PriceTo.Value)));
    }

    var searchResponse = await _searchOperation.SearchAsync<ProductIndex>(s => s
        .Query(q => q
            .Bool(b => b
                .Must(mustQueries)
            )
        )
    );

    return searchResponse.Documents.ToList();
}

That would use a lambda expression to add conditions dynamically to the must clauses of a Bool query. The SearchAsync method (or Search if you are not using asynchronous calls) accepts a lambda where you can define your query using the fluent API.

That constructs a List<Func<QueryContainerDescriptor<ProductIndex>, QueryContainer>>, where each Func<QueryContainerDescriptor<ProductIndex>, QueryContainer> represents a conditional query that should be applied if its corresponding condition is met (e.g., a search term is not null or empty, a category ID is specified, etc.). That list is then used to dynamically build a Boolean query that combines all the conditions using the .Must method.

Each condition is added as a lambda expression that describes how to build a query fragment:

if (!string.IsNullOrEmpty(searchDto.Term))
{
    mustQueries.Add(q => q.Match(m => m.Field(f => f.Description).Query(searchDto.Term)));
}
// Additional conditions are added in a similar manner

Finally, these conditional queries are combined into a single Boolean query when executing the search:

var searchResponse = await _searchOperation.SearchAsync<ProductIndex>(s => s
    .Query(q => q
        .Bool(b => b
            .Must(mustQueries)
        )
    )
);

By accumulating conditions into a List<Func<...>> and applying them within a .Bool(b => b.Must(...)) query, you make sure all relevant conditions are evaluated together in the final query. That makes it easier to add or remove query conditions dynamically based on the presence or absence of search criteria.

---

I was referencing the NuGet package version.
Nonetheless, the way to combine more than one query is to create a search request and inside the Query use the && with each query.

That would leverage the logical AND operator (&&) to combine multiple query conditions directly, without explicitly constructing a list of lambda expressions and passing them to a .Bool().Must() clause.

public async Task<List<ProductIndex>> Search(ProductSearchDto searchDto)
{
    // Initialize the base query to match all documents
    QueryContainer query = new MatchAllQuery(); 

    // Conditionally combine queries using the && operator
    if (!string.IsNullOrEmpty(searchDto.Term))
    {
        query &= new MatchQuery { Field = Infer.Field<ProductIndex>(f => f.Description), Query = searchDto.Term };
    }
    if (!string.IsNullOrEmpty(searchDto.CategoryId))
    {
        query &= new MatchQuery { Field = Infer.Field<ProductIndex>(f => f.CategoryId), Query = searchDto.CategoryId };
    }
    if (searchDto.Stars.HasValue)
    {
        query &= new TermQuery { Field = Infer.Field<ProductIndex>(f => f.Stars), Value = searchDto.Stars.Value };
    }
    if (searchDto.PriceFrom.HasValue && searchDto.PriceTo.HasValue)
    {
        query &= new RangeQuery { Field = Infer.Field<ProductIndex>(f => f.Price), GreaterThanOrEquals = searchDto.PriceFrom, LessThanOrEquals = searchDto.PriceTo };
    }

    var searchResponse = await _searchOperation.SearchAsync<ProductIndex>(s => s
        .Query(_ => query)
    );

    return searchResponse.Documents.ToList();
}

Each conditional check directly creates an instance of the appropriate query type (MatchQuery, TermQuery, RangeQuery, etc.) and combines it with the existing query using &= (as used here, equivalent to performing a logical AND between the current state of query and the new condition). That makes it clear what type of query is being used for each condition.