C# – Searching ElasticSearch using NEST C# Client

celasticsearchnest

I started looking around for a search engine and after some reading I decided going with ElasticSearch (which is quite amazing :)), my project is in C# so I looked around for a client and started using NEST, everything is quite straightforward but I am a bit confused on the searching part.

I want to search all fields on a specific type what I came up with is the following code:

elasticClient.Search<NewType>(s => s.Query(q => q.QueryString(d => d.Query(queryString))));

I saw that much of the string query search is deprecated and wanted to make sure the above is the correct way of doing this (the above is not marked as deprecated…) also it is a bit long for a simple task so maybe anyone knows another way of doing this.

Thanks

Best Answer

I just use the string query version: create my query object using C# anonymous type and serialize it to JSON.

That way, I can have straightforward mapping from all the JSON query examples out there, no need translating into this "query DSL".

Elasticsearch by itself evolves quite rapidly, and this query DSL thus is bound to lack some features.

Edit: Example:

var query = "blabla";
var q = new
        {
            query = new
            {
                text = new
                {
                    _all= query
                }
            }, 
            from = (page-1)*pageSize, 
            size=pageSize
        };
        var qJson = JsonConvert.SerializeObject(q);
        var hits = _elasticClient.Search<SearchItem>(qJson);

Related Solutions

C# – Should ‘using’ directives be inside or outside the namespace

There is actually a (subtle) difference between the two. Imagine you have the following code in File1.cs:

// File1.cs
using System;
namespace Outer.Inner
{
    class Foo
    {
        static void Bar()
        {
            double d = Math.PI;
        }
    }
}

Now imagine that someone adds another file (File2.cs) to the project that looks like this:

// File2.cs
namespace Outer
{
    class Math
    {
    }
}

The compiler searches Outer before looking at those using directives outside the namespace, so it finds Outer.Math instead of System.Math. Unfortunately (or perhaps fortunately?), Outer.Math has no PI member, so File1 is now broken.

This changes if you put the using inside your namespace declaration, as follows:

// File1b.cs
namespace Outer.Inner
{
    using System;
    class Foo
    {
        static void Bar()
        {
            double d = Math.PI;
        }
    }
}

Now the compiler searches System before searching Outer, finds System.Math, and all is well.

Some would argue that Math might be a bad name for a user-defined class, since there's already one in System; the point here is just that there is a difference, and it affects the maintainability of your code.

It's also interesting to note what happens if Foo is in namespace Outer, rather than Outer.Inner. In that case, adding Outer.Math in File2 breaks File1 regardless of where the using goes. This implies that the compiler searches the innermost enclosing namespace before it looks at any using directive.

Make elasticsearch only return certain fields

Yep, Use a better option source filter. If you're searching with JSON it'll look something like this:

{
    "_source": ["user", "message", ...],
    "query": ...,
    "size": ...
}

In ES 2.4 and earlier, you could also use the fields option to the search API:

{
    "fields": ["user", "message", ...],
    "query": ...,
    "size": ...
}

This is deprecated in ES 5+. And source filters are more powerful anyway!

Best Answer

Related Solutions

C# – Should ‘using’ directives be inside or outside the namespace

Make elasticsearch only return certain fields

Related Topic