Advanced Data Sources

Advanced Data Sources and Output Targets

This page covers patterns that go beyond the standard file-based workflow: reusing existing database connections, loading RDL from non-file sources, and streaming output to custom targets.

Loading RDL from non-file sources

RDLParser takes a plain string — the RDL XML. Anything that produces a string works.

From a database column

// Fetch the RDL XML from a database
await using var conn = new Microsoft.Data.SqlClient.SqlConnection(connectionString);
await conn.OpenAsync();
await using var cmd = conn.CreateCommand();
cmd.CommandText = "SELECT RdlXml FROM ReportTemplates WHERE Name = @name";
cmd.Parameters.AddWithValue("@name", "SalesReport");
var rdlXml = (string)await cmd.ExecuteScalarAsync();

// Parse and render as normal
var rdlp = new RDLParser(rdlXml) { Folder = @"C:\reports" };
using var report = await rdlp.Parse();

From an embedded resource

// report.rdl is an embedded resource in the assembly
var assembly = typeof(MyApp).Assembly;
using var stream = assembly.GetManifestResourceStream("MyApp.Reports.SalesReport.rdl")!;
using var reader = new StreamReader(stream);
var rdlXml = await reader.ReadToEndAsync();

var rdlp = new RDLParser(rdlXml);
using var report = await rdlp.Parse();

From a generated string

When using Programmatic Report Creation, Create.GenerateRdl returns a Report object directly — there is no intermediate file. For other programmatic cases:

string rdlXml = BuildReportDefinition();   // your RDL-generating method
var rdlp = new RDLParser(rdlXml);
using var report = await rdlp.Parse();

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Reusing an existing database connection

By default the engine opens its own connection using the connection string embedded in the RDL. To reuse an existing IDbConnection — for transaction support, connection pooling, or multi-tenant isolation — assign it to DataSource.UserConnection before calling RunGetData:

using Majorsilence.Reporting.Rdl;

RdlEngineConfig.RdlEngineConfigInit();

var rdlp = new RDLParser(await File.ReadAllTextAsync("report.rdl"));
using var report = await rdlp.Parse();

// Supply your own open connection
using var conn = new Microsoft.Data.SqlClient.SqlConnection(tenantConnectionString);
await conn.OpenAsync();

report.DataSources["DataSourceName"].UserConnection = conn;

await report.RunGetData(null);

The DataSource name must match the one defined in the report. Use the designer's Data → Data Sources menu to find it.

Use cases:

• Multi-tenant apps where the connection string is determined at request time
• Sharing a connection or transaction across multiple reports
• Avoiding repeated authentication round-trips when generating multiple reports in a batch

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Custom output targets with IStreamGen

OneFileStreamGen and MemoryStreamGen both implement IStreamGen. You can implement the interface to stream rendered output to any target without touching the disk.

public interface IStreamGen
{
    Stream GetStream();
    TextWriter GetTextWriter();
    Stream GetIOStream(out string relativeName, string extension);
    void CloseMainStream();
}

Example — stream to Azure Blob Storage

public sealed class AzureBlobStreamGen : IStreamGen, IDisposable
{
    private readonly MemoryStream _buffer = new();
    private readonly BlobClient _blob;

    public AzureBlobStreamGen(BlobClient blob) => _blob = blob;

    public Stream GetStream()    => _buffer;
    public TextWriter GetTextWriter() => new StreamWriter(_buffer);
    public Stream GetIOStream(out string relativeName, string extension)
    {
        relativeName = $"resource{extension}";
        return _buffer;
    }
    public void CloseMainStream() { }

    public async Task CommitAsync()
    {
        _buffer.Position = 0;
        await _blob.UploadAsync(_buffer, overwrite: true);
    }

    public void Dispose() => _buffer.Dispose();
}

// Usage
var blobClient = containerClient.GetBlobClient("reports/sales-2024.pdf");
await using var sg = new AzureBlobStreamGen(blobClient);
await report.RunRender(sg, OutputPresentationType.PDF);
await sg.CommitAsync();

Example — stream directly to an ASP.NET Core HttpResponse

Response.ContentType = "application/pdf";
Response.Headers["Content-Disposition"] = "attachment; filename=report.pdf";

// Use MemoryStreamGen, then copy — do not write directly to Response.Body
// while the report is still rendering, as RunRender may seek the stream.
using var ms = new MemoryStreamGen();
await report.RunRender(ms, OutputPresentationType.PDF);

var buffer = ((MemoryStream)ms.GetStream()).ToArray();
await Response.Body.WriteAsync(buffer);

See Streaming PDF — ASP.NET Core for the full controller pattern.

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Enumerating available data providers at runtime

string[] providers = RdlEngineConfig.GetProviders();
// e.g. ["Microsoft.Data.SqlClient", "PostgreSQL", "MySQL.NET", "Json", ...]

Useful for building dynamic connection dialogs or validating configuration at startup.

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Registering a custom report item at runtime

Custom report items (barcodes, charts, QR codes) are normally declared in RdlEngineConfig.xml. You can also register them in code:

RdlEngineConfig.DeclareNewCustomReportItem("MyCustomChart", typeof(MyCustomChartRenderer));

MyCustomChartRenderer must implement ICustomReportItem. This is useful for plugins and assemblies loaded at runtime.