如何使用C#在ASP.NET中从数据库检索PDF文件

using IronPdf;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Data.SqlClient;

[ApiController]
[Route("api/[controller]")]
public class PdfController : ControllerBase
{
    private readonly string _connectionString;

    public PdfController(IConfiguration configuration)
    {
        _connectionString = configuration.GetConnectionString("DefaultConnection")
            ?? throw new InvalidOperationException("Connection string not found.");
    }

    [HttpGet("{id}")]
    public async Task<IActionResult> GetPdf(int id)
    {
        byte[] pdfBytes = await RetrievePdfBytesAsync(id);
        if (pdfBytes is null || pdfBytes.Length == 0)
            return NotFound("PDF document not found.");

        // Load into IronPDF for validation or optional modification
        using var pdfDocument = new PdfDocument(pdfBytes);

        // Inline display -- browser opens PDF viewer
        Response.Headers.Append("Content-Disposition", "inline; filename=\"document.pdf\"");
        return File(pdfDocument.BinaryData, "application/pdf");
    }

    private async Task<byte[]> RetrievePdfBytesAsync(int documentID)
    {
        await using var connection = new SqlConnection(_connectionString);
        await connection.OpenAsync();

        const string query = "SELECT 文件内容 FROM PdfDocuments WHERE ID = @ID";
        await using var command = new SqlCommand(query, connection);
        command.Parameters.AddWithValue("@ID", documentID);

        var result = await command.ExecuteScalarAsync();
        return result as byte[] ?? Array.Empty<byte>();
    }
}

Imports IronPdf
Imports Microsoft.AspNetCore.Mvc
Imports Microsoft.Data.SqlClient

<ApiController>
<Route("api/[controller]")>
Public Class PdfController
    Inherits ControllerBase

    Private ReadOnly _connectionString As String

    Public Sub New(configuration As IConfiguration)
        _connectionString = configuration.GetConnectionString("DefaultConnection")
        If _connectionString Is Nothing Then
            Throw New InvalidOperationException("Connection string not found.")
        End If
    End Sub

    <HttpGet("{id}")>
    Public Async Function GetPdf(id As Integer) As Task(Of IActionResult)
        Dim pdfBytes As Byte() = Await RetrievePdfBytesAsync(id)
        If pdfBytes Is Nothing OrElse pdfBytes.Length = 0 Then
            Return NotFound("PDF document not found.")
        End If

        ' Load into IronPDF for validation or optional modification
        Using pdfDocument As New PdfDocument(pdfBytes)
            ' Inline display -- browser opens PDF viewer
            Response.Headers.Append("Content-Disposition", "inline; filename=""document.pdf""")
            Return File(pdfDocument.BinaryData, "application/pdf")
        End Using
    End Function

    Private Async Function RetrievePdfBytesAsync(documentID As Integer) As Task(Of Byte())
        Await Using connection As New SqlConnection(_connectionString)
            Await connection.OpenAsync()

            Const query As String = "SELECT 文件内容 FROM PdfDocuments WHERE ID = @ID"
            Await Using command As New SqlCommand(query, connection)
                command.Parameters.AddWithValue("@ID", documentID)

                Dim result = Await command.ExecuteScalarAsync()
                Return If(TryCast(result, Byte()), Array.Empty(Of Byte)())
            End Using
        End Using
    End Function
End Class

[HttpGet("download/{id}")]
public async Task<IActionResult> DownloadPdf(int id)
{
    await using var connection = new SqlConnection(_connectionString);
    await connection.OpenAsync();

    const string query = "SELECT 文件名, 文件内容 FROM PdfDocuments WHERE ID = @ID";
    await using var command = new SqlCommand(query, connection);
    command.Parameters.AddWithValue("@ID", documentID);

    await using var reader = await command.ExecuteReaderAsync();
    if (!await reader.ReadAsync())
        return NotFound("Document not found.");

    var fileName = reader.GetString(reader.GetOrdinal("文件名"));
    var pdfBytes = (byte[])reader["文件内容"];

    using var pdfDocument = new PdfDocument(pdfBytes);
    return File(pdfDocument.BinaryData, "application/pdf", fileName);
}

Imports System.Data.SqlClient
Imports Microsoft.AspNetCore.Mvc

<HttpGet("download/{id}")>
Public Async Function DownloadPdf(id As Integer) As Task(Of IActionResult)
    Await Using connection As New SqlConnection(_connectionString)
        Await connection.OpenAsync()

        Const query As String = "SELECT 文件名, 文件内容 FROM PdfDocuments WHERE ID = @ID"
        Await Using command As New SqlCommand(query, connection)
            command.Parameters.AddWithValue("@ID", id)

            Await Using reader = Await command.ExecuteReaderAsync()
                If Not Await reader.ReadAsync() Then
                    Return NotFound("Document not found.")
                End If

                Dim fileName As String = reader.GetString(reader.GetOrdinal("文件名"))
                Dim pdfBytes As Byte() = CType(reader("文件内容"), Byte())

                Using pdfDocument As New PdfDocument(pdfBytes)
                    Return File(pdfDocument.BinaryData, "application/pdf", fileName)
                End Using
            End Using
        End Using
    End Using
End Function

[HttpGet("watermarked/{id}")]
public async Task<IActionResult> GetWatermarkedPdf(int id)
{
    byte[] pdfBytes = await RetrievePdfBytesAsync(id);
    if (pdfBytes is null || pdfBytes.Length == 0)
        return NotFound("PDF document not found.");

    using var pdfDocument = new PdfDocument(pdfBytes);

    // HTML watermark applied to every page
    string watermarkHtml = "<h2 style='color:red; opacity:0.4; font-family:Arial;'>CONFIDENTIAL</h2>";
    pdfDocument.ApplyWatermark(
        watermarkHtml,
        rotation: 30,
        verticalAlignment: VerticalAlignment.Middle,
        horizontalAlignment: HorizontalAlignment.Center
    );

    return File(pdfDocument.BinaryData, "application/pdf");
}

Imports Microsoft.AspNetCore.Mvc

<HttpGet("watermarked/{id}")>
Public Async Function GetWatermarkedPdf(id As Integer) As Task(Of IActionResult)
    Dim pdfBytes As Byte() = Await RetrievePdfBytesAsync(id)
    If pdfBytes Is Nothing OrElse pdfBytes.Length = 0 Then
        Return NotFound("PDF document not found.")
    End If

    Using pdfDocument As New PdfDocument(pdfBytes)
        ' HTML watermark applied to every page
        Dim watermarkHtml As String = "<h2 style='color:red; opacity:0.4; font-family:Arial;'>CONFIDENTIAL</h2>"
        pdfDocument.ApplyWatermark(
            watermarkHtml,
            rotation:=30,
            verticalAlignment:=VerticalAlignment.Middle,
            horizontalAlignment:=HorizontalAlignment.Center
        )

        Return File(pdfDocument.BinaryData, "application/pdf")
    End Using
End Function