Generate documents from templates with GroupDocs.Assembly Leave feedback
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GroupDocs.Assembly generates documents from a template and a data source. Unlike the rest of the suite it needs an input you have to author yourself: a template carrying <<[...]>> tags that say where the data goes.
Every example below uses invoice-template.docx, which contains:
Invoice <<[invoice.Number]>>
Bill to: <<[invoice.CustomerName]>>
Date: <<[invoice.Date]:"dd MMMM yyyy">>
Items
<<foreach [item in invoice.Items]>><<[item.Description]>> - qty <<[item.Quantity]>> - <<[item.Price]>> USD<</foreach>>
Total: <<[invoice.Items.Sum(i => i.Quantity * i.Price)]>> USD
The tag syntax is the LINQ Reporting Engine: <<[expr]>> inserts a value, <<foreach [x in xs]>>…<</foreach>> repeats a block, and expressions can compute — note the Sum in the total.
Pass any object as a data source and name it. The name is what the template’s tags refer to — here invoice.
using System;
using System.Collections.Generic;
using GroupDocs.Assembly;
public class InvoiceItem
{
public string Description { get; set; } = "";
public int Quantity { get; set; }
public decimal Price { get; set; }
}
public class Invoice
{
public string Number { get; set; } = "";
public string CustomerName { get; set; } = "";
public DateTime Date { get; set; }
public List<InvoiceItem> Items { get; set; } = new();
}
var invoice = new Invoice
{
Number = "INV-2026-0042",
CustomerName = "Northwind Trading Ltd",
Date = new DateTime(2026, 7, 16),
Items = new List<InvoiceItem>
{
new InvoiceItem { Description = "Document processing licence", Quantity = 3, Price = 1200m },
new InvoiceItem { Description = "Priority support", Quantity = 1, Price = 800m },
new InvoiceItem { Description = "Onboarding workshop", Quantity = 2, Price = 450m }
}
};
DocumentAssembler assembler = new DocumentAssembler();
// "invoice" must match the name the template's tags use
assembler.AssembleDocument(
"invoice-template.docx",
"assembly-from-objects.docx",
new DataSourceInfo(invoice, "invoice"));
Console.WriteLine("Generated assembly-from-objects.docx");
invoice-template.docx is the template used in this example. Click here to download it.
Binary file (DOCX, 12 KB)
The output format follows the output file’s extension. The same template and the same data produce a PDF instead of a Word file with no other change.
using System;
using System.Collections.Generic;
using GroupDocs.Assembly;
// Data classes must be public — see the note below
public class LineItem
{
public string Description { get; set; } = "";
public int Quantity { get; set; }
public decimal Price { get; set; }
}
public class Order
{
public string Number { get; set; } = "";
public string CustomerName { get; set; } = "";
public DateTime Date { get; set; }
public List<LineItem> Items { get; set; } = new();
}
var invoice = new Order
{
Number = "INV-2026-0043",
CustomerName = "Contoso Manufacturing",
Date = new DateTime(2026, 7, 16),
Items = new List<LineItem>
{
new LineItem { Description = "Annual subscription", Quantity = 1, Price = 9600m },
new LineItem { Description = "Additional seats", Quantity = 5, Price = 240m }
}
};
DocumentAssembler assembler = new DocumentAssembler();
assembler.AssembleDocument(
"invoice-template.docx",
"assembly-to-pdf.pdf",
new DataSourceInfo(invoice, "invoice"));
Console.WriteLine("Generated assembly-to-pdf.pdf");
invoice-template.docx is the template used in this example. Click here to download it.
Binary file (PDF, 91 KB)
WarningData source classes must be public. The engine reflects over the object at generation time, so an anonymous type or an
internalclass fails at run time rather than compile time:System.InvalidOperationException: A data source object must be of a visible type or implement 'System.Collections.IEnumerable'. (Parameter 'dataSource')The same applies to the item type inside a collection —
List<LineItem>needsLineItempublic too.
GroupDocs.Assembly also reads JSON, XML, CSV, DataTable and database data sources, generates tables and charts from collections, supports conditional blocks, master-detail reports, hyperlinks and images in templates, and can produce output in any format the suite supports.
- GroupDocs.Assembly for .NET documentation — the full product guide
- Template syntax
- API reference
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