MetadataDefaults Class

Overview

The MetadataDefaults class provides default values based on POCO DataSet column metadata. It is typically used when creating new rows in schema-driven scenarios to initialize each cell with an appropriate default value based on a column’s data type token (for example, values from DataTypeNames) and nullability.

The default selection rules implemented by MetadataDefaults are:

• For string columns, the default value is string.Empty (even when nullable).
• For nullable columns (except string), the default value is null.
• For non-nullable binary columns (DataTypeNames.BINARY), the default value is an empty byte array.
• For non-nullable numeric, boolean, date/time, and GUID types, the default value is the CLR default (for example, 0, false, default(DateTime), Guid.Empty).
• For logical tokens such as JSON, SPATIAL, and OBJECT, the default value is null.

Namespace and Assembly

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

Declaration

public static class MetadataDefaults
{
    public static object? GetDefaultValue(string? dataType, bool isNullable);
}

Public Methods

• object? GetDefaultValue(string dataType, bool isNullable)
  Returns a default value based on a data type name (for example, "String", "Int32", "Boolean") and a nullability flag. For non-nullable value types, it returns an appropriate default instance; for nullable types, it typically returns null. The method includes logic to interpret common .NET type names and safely handles invalid input by returning null in ambiguous cases.

Usage Example

// 1. Compute defaults using type tokens and nullability
object? nameDefault = MetadataDefaults.GetDefaultValue(DataTypeNames.STRING, isNullable: true);
object? idDefault = MetadataDefaults.GetDefaultValue(DataTypeNames.INT32, isNullable: false);
object? optionalGuidDefault = MetadataDefaults.GetDefaultValue(DataTypeNames.GUID, isNullable: true);

// 2. Typical usage: create a row with defaults using DataRowFactory
IDataSet dataSet = DataSetFactory.CreateDataSet();
IDataTable departmentDataTable = dataSet.AddNewTable("Department");
departmentDataTable.AddColumn("Id", DataTypeNames.INT32);
departmentDataTable.AddColumn("Name", DataTypeNames.STRING);

IDataRow departmentDataRow = DataRowFactory.CreateFromColumnsWithDefaults(departmentDataTable.Columns);

Remarks

• If dataType is null or empty, GetDefaultValue returns null.
• Unknown or unsupported data type tokens return null.
• The rules are intentionally conservative for logical types (JSON, spatial, object) to avoid guessing a default structure.

 

Table of Content POCO DataSet PocoDataSet.Data

 

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Business Process Programming in .Net
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