BuildPrimaryKeyIndex Method

Overview

The BuildPrimaryKeyIndex method builds an in-memory primary key index of rows in a table using the table's primary key values. The returned dictionary maps a compiled primary-key string to the corresponding data row.

This method is primarily used by merge logic (for example, when matching rows between two tables), and it is especially useful for composite primary keys.

Declaration

/// <summary>
/// </summary>
/// </summary>
/// <param name="dataTable">Data table</param>
/// <param name="primaryKeyColumnNames">Primary key column names</param>
/// <returns>Built primary key index</returns>
public static Dictionary<string, IDataRow> BuildPrimaryKeyIndex(this IDataTable? dataTable, List<string> primaryKeyColumnNames)

Namespace and Assembly

Namespace: PocoDataSet.Extensions
Assembly: PocoDataSet.Extensions.dll

Behavior

• Creates a dictionary with StringComparer.Ordinal for key comparison (case-sensitive).
• If dataTable is null, returns an empty dictionary.
• Iterates through dataTable.Rows and computes a key for each row by calling dataRow.CompilePrimaryKeyValue(primaryKeyColumnNames).
• If the compiled key is not already present in the dictionary, adds the row to the primary key index. If a duplicate key is encountered, the first row wins and the duplicate is ignored.

Primary Key Compilation Format

The exact key format is determined by CompilePrimaryKeyValue:

Length of the primary key field value + "#" + primary key field value + "|" +
length of the primary key field value + "#" + primary key field value + "|" + ...

This format allows unambiguous concatenation for composite keys (for example, key parts "12" and "3" do not collide with "1" and "23").

Usage Example

The following example builds a row primary key index for a refreshed table and uses it to look up matching rows from a current table during a merge-like comparison:

// 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
IDataRow employeeDataRow1 = employeeTable.AddNewRow();
employeeDataRow1["Id"] = 1;
employeeDataRow1["FirstName"] = "John";
employeeDataRow1["LastName"] = "Doe";

IDataRow employeeDataRow2 = employeeTable.AddNewRow();
employeeDataRow2["Id"] = 2;
employeeDataRow2["FirstName"] = "Sara";
employeeDataRow2["LastName"] = "Gor";

// 4. Build primary key index for refreshed rows
Dictionary<string, IDataRow> employeeTablePrimaryKeyIndex = employeeTable.BuildPrimaryKeyIndex(employeeTable.PrimaryKeys);

// 5. Get data rows by its indexes
IDataRow firstDataRow = employeeTablePrimaryKeyIndex["1#1"];
IDataRow secondDataRow = employeeTablePrimaryKeyIndex["1#2"];

Notes

• This overload does not take a scope predicate. If you need to primary key index only a subset of rows, filter rows before calling this method (for example, build a temporary list of rows or introduce a scoped overload).
• Duplicate compiled keys indicate either duplicate primary key values in the table or an incorrect primary key column list. In such cases, only the first row with a given key is stored in the primary key index.

 

Table of Content POCO DataSet DataTable Extensions Group DataTable Members

 

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Business Process Programming in .Net
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