RequestAttribute

[Request] attribute indicates that if a field contains a value that implements IRequest or IRecord, it will be resolved before processing the query further.

public record Sum([Request] object a, [Request] object b) : IRequestFor<int>;

[RequestArray] indicates that if a field contains a value that implements IEnumerable of IRequest or IRecord, it will be resolved before processing the query further.

public record Sum([RequestArray] object values) : IRequestFor<int>;

Using both attributes together indicates that field may contain a request for an array whose elements are to be resolved.

public record Sum([Request, RequestArray] object values) : IRequestFor<int>;

Service must have ServiceHandlers or its subcomponent RequestHandlers for resolve to work.

IService service = Services.Create((new StringJoinHandler(), RequestHandlers.Instance, RequestResolverAsync.Instance));

IService service = Services.Create((new StringJoinHandler(), ServiceHandlers.Instance));

In the following example, a handler concatenates strings with separator. Field-requests are resolved before handler is invoked.

// Create service
IService service = Services.Create((RequestHandlers.Instance, new StringJoinHandler()));
// Create request
IRequestFor<string> joinRequest = new StringJoinRequest(", ", "Hello", new StringJoinRequest("+", "World", "Sphere"));
// Print request
WriteLine(joinRequest.PrintTree());
// StringJoinRequest
// ├── Separator = ", "
// ├── Strings[0] = "Hello"
// └── Strings[1] = StringJoinRequest
//     ├── Separator = "+"
//     ├── Strings[0] = "World"
//     └── Strings[1] = "Sphere"
// Execute request
string joinText = service.GetRequired<IRequestFor<string>, string>(joinRequest);
// Print join
Console.WriteLine(joinText); // "Hello, World+Sphere"

/// <summary>Join strings with <see cref="String.Join"/></summary>
public record StringJoinRequest : IRequestFor<string>
{
    /// <summary>Separator string, <see cref="String"/>, <![CDATA[IRequestFor<string>]]></summary>
    [Request]
    public object Separator { get; init; }

    /// <summary>Strings to join as array</summary>
    [Request, RequestArray]
    public object Strings { get; init; }

    /// <summary>Create request</summary>
    public StringJoinRequest(object separator, params object[] strings)
    {
        Separator = separator;
        Strings = strings;
    }
}

/// <summary>Join strings</summary>
public class StringJoinHandler : IHandler<StringJoinRequest, string>
{
    /// <summary>Join strings</summary>
    public void Handle(IQuery<StringJoinRequest, string> query)
    {
        // Handled
        if (query.Handled()) return;
        // Get separator
        if (query.Request.Separator is not string separator) return;
        // Get strings
        if (query.Request.Strings is not Array strings) return;
        // Create builder
        StringBuilder sb = new StringBuilder();
        // 
        for (int i = 0; i < strings.Length; i++)
        {
            // Append separator
            if (i > 0) sb.Append(separator);
            // Get value
            string? value = strings.GetValue(i)?.ToString();
            // Append string
            if (value != null) sb.Append(value);
        }
        // Build text
        string text = sb.ToString();
        // Assign result
        query.Response.SetValue(text);
    }
}

Full Example

Full example

using System;
using System.Text;
using Avalanche.Service;
using Avalanche.Utilities.Record;
using static System.Console;

public class request_requestattribute
{
    public static void Run()
    {
        {
            // <01>
            IService service = Services.Create((new StringJoinHandler(), RequestHandlers.Instance, RequestResolverAsync.Instance));
            // </01>
        }
        {
            // <02>
            IService service = Services.Create((new StringJoinHandler(), ServiceHandlers.Instance));
            // </02>
        }
        {
            // <03>
            // Create service
            IService service = Services.Create((RequestHandlers.Instance, new StringJoinHandler()));
            // Create request
            IRequestFor<string> joinRequest = new StringJoinRequest(", ", "Hello", new StringJoinRequest("+", "World", "Sphere"));
            // Print request
            WriteLine(joinRequest.PrintTree());
            // StringJoinRequest
            // ├── Separator = ", "
            // ├── Strings[0] = "Hello"
            // └── Strings[1] = StringJoinRequest
            //     ├── Separator = "+"
            //     ├── Strings[0] = "World"
            //     └── Strings[1] = "Sphere"
            // Execute request
            string joinText = service.GetRequired<IRequestFor<string>, string>(joinRequest);
            // Print join
            Console.WriteLine(joinText); // "Hello, World+Sphere"
            // </03>
        }
    }

    static class _10
    {
        // <10>
        public record Sum([Request] object a, [Request] object b) : IRequestFor<int>;
        // </10>
    }
    static class _11
    {
        // <11>
        public record Sum([RequestArray] object values) : IRequestFor<int>;
        // </11>
    }
    static class _12
    {
        // <12>
        public record Sum([Request, RequestArray] object values) : IRequestFor<int>;
        // </12>
    }

    // <13>
    /// <summary>Join strings with <see cref="String.Join"/></summary>
    public record StringJoinRequest : IRequestFor<string>
    {
        /// <summary>Separator string, <see cref="String"/>, <![CDATA[IRequestFor<string>]]></summary>
        [Request]
        public object Separator { get; init; }

        /// <summary>Strings to join as array</summary>
        [Request, RequestArray]
        public object Strings { get; init; }

        /// <summary>Create request</summary>
        public StringJoinRequest(object separator, params object[] strings)
        {
            Separator = separator;
            Strings = strings;
        }
    }
    // </13>

    // <14>
    /// <summary>Join strings</summary>
    public class StringJoinHandler : IHandler<StringJoinRequest, string>
    {
        /// <summary>Join strings</summary>
        public void Handle(IQuery<StringJoinRequest, string> query)
        {
            // Handled
            if (query.Handled()) return;
            // Get separator
            if (query.Request.Separator is not string separator) return;
            // Get strings
            if (query.Request.Strings is not Array strings) return;
            // Create builder
            StringBuilder sb = new StringBuilder();
            // 
            for (int i = 0; i < strings.Length; i++)
            {
                // Append separator
                if (i > 0) sb.Append(separator);
                // Get value
                string? value = strings.GetValue(i)?.ToString();
                // Append string
                if (value != null) sb.Append(value);
            }
            // Build text
            string text = sb.ToString();
            // Assign result
            query.Response.SetValue(text);
        }
    }
    // </14>
}