Marten.AspNetCore #

In Marten V4, there is a small new addon that adds helpers for ASP.Net Core development, expressly the ability to very efficiently stream the raw JSON of persisted documents straight to an HTTP response without every having to waste time with deserialization/serialization or even reading the data into a JSON string in memory.

First, to get started, Marten provides Marten.AspNetCore plugin.

Install it through the Nuget package.

PM> Install-Package Marten.AspNetCore

Single Document #

If you need to write a single Marten document to the HTTP response by its id, the most efficient way is this syntax shown in a small sample MVC Core controller method:

[HttpGet("/issue/{issueId}")]
public Task Get(Guid issueId, [FromServices] IQuerySession session)
{
    // This "streams" the raw JSON to the HttpResponse
    // w/o ever having to read the full JSON string or
    // deserialize/serialize within the HTTP request
    return session.Json
        .WriteById<Issue>(issueId, HttpContext);
}

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That syntax will write the HTTP content-type and content-length response headers as you'd expect, and copy the raw JSON for the document to the HttpResponse.Body stream if the document is found. The status code will be 200 if the document is found, and 404 if it is not.

Likewise, if you need to write a single document from a Linq query, you have this syntax:

[HttpGet("/issue2/{issueId}")]
public Task Get2(Guid issueId, [FromServices] IQuerySession session)
{
    return session.Query<Issue>().Where(x => x.Id == issueId)
        .WriteSingle(HttpContext);
}

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Multiple Documents #

The WriteArray() extension method will allow you to write an array of documents in a Linq query to the outgoing HTTP response like this:

[HttpGet("/issue/open")]
public Task OpenIssues([FromServices] IQuerySession session)
{
    // This "streams" the raw JSON to the HttpResponse
    // w/o ever having to read the full JSON string or
    // deserialize/serialize within the HTTP request
    return session.Query<Issue>()
        .Where(x => x.Open)
        .WriteArray(HttpContext);
}

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Compiled Query Support #

The absolute fastest way to invoke querying in Marten is by using compiled queries that allow you to use Linq queries without the runtime overhead of continuously parsing Linq expressions every time.

Back to the sample endpoint above where we write an array of all the open issues. We can express the same query in a simple compiled query like this:

public class OpenIssues: ICompiledListQuery<Issue>
{
    public Expression<Func<IMartenQueryable<Issue>, IEnumerable<Issue>>> QueryIs()
    {
        return q => q.Where(x => x.Open);
    }
}

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And use that in an MVC Controller method like this:

[HttpGet("/issue2/open")]
public Task OpenIssues2([FromServices] IQuerySession session)
{
    return session.WriteArray(new OpenIssues(), HttpContext);
}

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Likewise, you could use a compiled query to write a single document. As a contrived sample, here's an example compiled query that reads a single Issue document by its id:

public class IssueById: ICompiledQuery<Issue, Issue>
{
    public Expression<Func<IMartenQueryable<Issue>, Issue>> QueryIs()
    {
        return q => q.FirstOrDefault(x => x.Id == Id);
    }

    public Guid Id { get; set; }
}

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And the usage of that to write JSON directly to the HttpContext in a controller method:

[HttpGet("/issue3/{issueId}")]
public Task Get3(Guid issueId, [FromServices] IQuerySession session)
{
    return session.Query<Issue>().Where(x => x.Id == issueId)
        .WriteSingle(HttpContext);
}

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