AddColumn Method

Overview

The AddColumn method adds a new column to the table schema.

If the table already contains rows, the method back-fills the newly added column into each existing row so that the row value dictionaries remain aligned with the schema.

Declaration

/// <summary>
/// Adds column
/// </summary>
/// <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>
/// <returns>Added column</returns>
public IColumnMetadata AddColumn(string columnName, string dataType, bool? isNullable = null, bool? isPrimaryKey = null, bool? isForeignKey = null)

Namespace and Assembly

Namespace: PocoDataSet.Data
Assembly: PocoDataSet.Data.dll

Behavior

• Throws InvalidOperationException if a column with the same name already exists in the table schema.
• Creates column metadata via the table schema (_dataTableSchema.CreateColumn).
• Ensures existing rows have the new column key (adds null when missing).
• Adds the column to the schema (_dataTableSchema.AddColumn).

Usage Example

// 1. Create an empty data set and a table
IDataSet dataSet = DataSetFactory.CreateDataSet();
IDataTable employeeTable = dataSet.AddNewTable("Employee");
employeeTable.AddColumn("Id", DataTypeNames.INT32);
employeeTable.AddColumn("FirstName", DataTypeNames.STRING);
employeeTable.AddColumn("LastName", DataTypeNames.STRING);

// 2. Add several rows to Employee data table
IDataRow employeeDataRow1 = employeeTable.AddNewRow();
employeeDataRow1["Id"] = 1;
employeeDataRow1["FirstName"] = "John";
employeeDataRow1["LastName"] = "Doe";

// Later, evolve schema by adding a new column after rows exist
employeeTable.AddColumn("NickName", DataTypeNames.STRING);

// The existing row has the new column key with null value
object? nick = employeeDataRow1["NickName"];

Notes

• Back-filling existing rows skips floating (sparse) rows (IFloatingDataRow) to preserve sparsity semantics.
• Primary key membership is expressed via IColumnMetadata.IsPrimaryKey.
• There is also an overload AddColumn(IColumnMetadata columnMetadata) that adds an already-constructed metadata instance.

 

Table of Content POCO DataSet API References POCO DataSet Types DataTable Members

 

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Business Process Programming in .Net
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