Whether your data lives in business objects, a database, a JSON file or an XML export, MailMerge can merge it, and a template works with every kind as long as the names and the hierarchy match. Each kind of data has its own merge method, can be offered in the Reporting tab for template design and, for databases, can be described by a data source configuration file, a feature of Windows Forms applications.

How Data Reaches a Template

Two classes handle data, for two purposes:

MailMerge merges it. Its merge methods take the data and fill the template in a TextControl or ServerTextControl.
DataSourceManager describes it. The DataSourceManager of the Reporting tab loads the same kinds of data, analyzes their tables, columns and relations and fills the drop-downs that users insert fields and blocks with.

Every kind of data ends up as tables: the records you merge form the master table, whose columns fill merge fields, and nested collections or related tables fill merge blocks. Overview explains this model.

Data	Merge with	Load for design with	Page
A business object or a collection of them, dictionaries	MergeObject, MergeObjects	`LoadSingleObject`, `LoadObjects`, `LoadAssembly`	Objects and Collections
A `DataTable`, or a `DataSet` with relations	Merge	`LoadDataTable`, `LoadDataSet`, a database connection	DataSets and DataTables
A JSON string	MergeJsonData	`LoadJson`	JSON and XML
An XML file or string	`Merge`, after `DataSet.ReadXml`	`LoadXmlFile`, `LoadXmlString`	JSON and XML
A database described by a configuration file	`Merge()` with `ReportDataSourceConfigFile`	`LoadDataSourceConfig`	Data Source Configuration Files

Data Sources in the Reporting Tab

Users choose the data for template design in the Select Data Source drop-down of the Reporting tab, which connects a database or opens an XML file, a JSON file or an assembly, as Data Source in Reporting Ribbon and Dialog Boxes shows. Your code loads data for the users instead, typically in the Load event of the form, as the Getting Started tutorial Create a Template does with invoice.json. The data used for design only needs the structure of the real data; the template is merged later with any data of that structure.

Choose a Data Source

If your data is	Use
Classes of your application, or data you query into objects	Business objects: Objects and Collections
Rows from a database in ADO.NET form	A `DataSet` with relations: DataSets and DataTables
The response of a web service, a file from another system	JSON or XML: JSON and XML
A database that templates should query by themselves	A configuration file: Data Source Configuration Files

Business objects and JSON are the most direct choices for new applications: they carry the hierarchy of the document without extra relations.

Pages in This Section

Objects and Collections: merge business objects, dictionaries and anonymous objects, control names with attributes.
DataSets and DataTables: merge tables with relations and connect a database in the Reporting tab.
JSON and XML: merge JSON, handle invalid JSON, read XML into a DataSet and set parsing cultures.
Data Source Configuration Files: save a database connection with its relations and merge templates with it.