AddColumn Method

Overview

The AddColumn method adds a column definition (IColumnMetadata) to an observable data table. In addition to adding metadata, it also ensures that all existing rows in the table receive the new column (with an appropriate default value).

The method supports optional flags for nullability, primary key, and foreign key. When these flags are not provided, the method applies simple conventions based on the column name (for example, treating Id as a primary key, and treating columns that end with Id as foreign keys).

Declaration

/// <summary>
/// Adds a column to observable table (delegates to inner table)
/// </summary>
/// <param name="observableDataTable">Observable data table</param>
/// <param name="columnName">Column name</param>
/// <param name="dataType">Data type</param>
/// <param name="isNullable">Flag indicating whether column is nullable</param>
/// <param name="isPrimaryKey">Flag indicating whether column is primary key</param>
/// <param name="isForeignKey">Flag indicating whether column is foreign key</param>
public static void AddColumn(this IObservableDataTable? dataTable, string columnName, string dataType, bool? isNullable = null, bool? isPrimaryKey = null, bool? isForeignKey = null)

Namespace and Assembly

Namespace: PocoDataSet.ObservableExtensions
Assembly: PocoDataSet.ObservableExtensions.dll

Behavior

• If dataTable is null, returns immediately.
• Validates columnName and dataType.
• Checks for duplicate column names by scanning dataTable.Columns. If a column with the same name exists, throws KeyDuplicationException.
• Creates a new ColumnMetadata and assigns:
  • ColumnName
  • DataType
• Primary key inference:
  • If isPrimaryKey is provided, uses it.
  • Otherwise, sets IsPrimaryKey = true only when columnName is exactly "Id".
• Nullability inference:
  • If isNullable is provided, uses it.
  • Otherwise, sets IsNullable = false for primary key columns; for other columns, defaults to true.
• Foreign key inference:
  • If isForeignKey is provided, uses it.
  • Otherwise, for non-primary-key columns, sets IsForeignKey = true when columnName ends with "Id" (case-sensitive, ordinal comparison) and is not exactly "Id".
• If the column is a foreign key (by override or inference), the method also assigns:
  • ReferencedColumnName = "Id"
  • ReferencedTableName as columnName without the trailing "Id" suffix
  For example, DepartmentId will reference table Department, column Id.
• Adds the column metadata to dataTable.Columns and calls EnsureExistingRowsHaveColumn(dataTable, columnName) to extend all existing rows with the new column.

Usage Examples

Add several columns using name-based inference:

// 1. Create observable data set
IObservableDataSet observableDataSet = new ObservableDataSet();

// 2. Create Employee observable table
IObservableDataTable employeeObservableDataTable = observableDataSet.AddNewTable("Employee");

// 3) Add columns
// - "Id" becomes a primary key, non-nullable
IColumnMetadata idColumnMetadata = employeeObservableDataTable.AddColumn("Id", DataTypeNames.INT32);

// - "FirstName" is nullable by default (unless overridden)
IColumnMetadata firstNameColumnMetadata = employeeObservableDataTable.AddColumn("FirstName", DataTypeNames.STRING);

// - "EmployeeTypeId" becomes a foreign key by convention
IColumnMetadata employeeTypeIdColumnMetadata = employeeObservableDataTable.AddColumn("EmployeeTypeId", DataTypeNames.INT32);

// Adds a non-nullable foreign key column, "SecurityLevelId"
IColumnMetadata securityLevelIdColumnMetadata = employeeObservableDataTable.AddColumn("SecurityLevelId", DataTypeNames.INT32, false, false, true);

Notes

• Column inference rules are intentionally simple. For rich relational metadata (such as explicit constraints, multi-column keys, or relationships spanning multiple columns), prefer supplying a complete IColumnMetadata yourself or using schema-loading APIs.
• Because EnsureExistingRowsHaveColumn is invoked, adding a column to a table with many existing rows may have a performance impact. (Each existing row is extended with the new column.)

 

Table of Content POCO DataSet Observable Data Table Members

 

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Business Process Programming in .Net
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