Extended Property Names Feature

This will be released in v3.12.0

This feature enhancement allows you to access database extended properties by their name in addition to their value. Previously, only the extended property value was available as a string in column.ExtendedProperty. Now you can access individual extended properties by name using the new column.ExtendedProperties dictionary.

How to Use

SQL Server Setup

First, add extended properties to your database column:

-- Add a JsonPropertyName extended property to a column
EXEC sp_addextendedproperty 
    @name = N'JsonPropertyName', 
    @value = N'id', 
    @level0type = N'SCHEMA', 
    @level0name = N'dbo', 
    @level1type = N'TABLE', 
    @level1name = N'YourTable', 
    @level2type = N'COLUMN', 
    @level2name = N'SystemId'

-- You can add multiple extended properties to the same column
EXEC sp_addextendedproperty 
    @name = N'CustomValidator', 
    @value = N'EmailValidator', 
    @level0type = N'SCHEMA', 
    @level0name = N'dbo', 
    @level1type = N'TABLE', 
    @level1name = N'YourTable', 
    @level2type = N'COLUMN', 
    @level2name = N'EmailAddress'

Code Generation Setup

In your .tt file or Settings.cs, use the UpdateColumn delegate:

Settings.UpdateColumn = delegate (Column column, Table table, List<EnumDefinition> enumDefinitions, List<JsonColumnMapping> jsonColumnMappings)
{
    // ...
    Settings.ApplyColumnCustomizations(column, table, enumDefinitions, jsonColumnMappings);
};

Generated Code Example

Given the SQL setup above, the generated code will look like:

public class YourTable
{
    [JsonPropertyName("id")]
    public string SystemId { get; set; }

    [CustomValidator(typeof(EmailValidator))]
    public string EmailAddress { get; set; }
}

Supported Databases

Database	Extended Property Name Support	Notes
SQL Server	✅ Yes	Reads actual extended property names from sys.extended_properties
PostgreSQL	⚠️ Placeholder	Uses 'Comment' as property name (PostgreSQL only has generic column comments)
SQL Server CE	⚠️ Placeholder	Uses 'ExtendedProperty' as property name
MySQL	❌ No	Does not support extended properties
Oracle	❌ No	Does not support extended properties
SQLite	❌ No	Does not support extended properties

Use Cases

1. JSON Property Mapping: Map database column names to different JSON property names
2. Custom Validation: Specify validators via extended properties
3. API Visibility: Control which properties appear in APIs
4. Documentation: Store property-specific documentation by category
5. Feature Flags: Enable/disable features per column
6. Custom Attributes: Add any custom attributes based on extended properties

Example: Multiple Extended Properties on One Column

-- Add multiple extended properties to one column
EXEC sp_addextendedproperty @name = N'JsonPropertyName', @value = N'userId', 
    @level0type = N'SCHEMA', @level0name = N'dbo', 
    @level1type = N'TABLE', @level1name = N'Orders', 
    @level2type = N'COLUMN', @level2name = N'UserId'

EXEC sp_addextendedproperty @name = N'Validator', @value = N'Required|Guid', 
    @level0type = N'SCHEMA', @level0name = N'dbo', 
    @level1type = N'TABLE', @level1name = N'Orders', 
    @level2type = N'COLUMN', @level2name = N'UserId'

EXEC sp_addextendedproperty @name = N'Description', @value = N'The unique identifier for the user', 
    @level0type = N'SCHEMA', @level0name = N'dbo', 
    @level1type = N'TABLE', @level1name = N'Orders', 
    @level2type = N'COLUMN', @level2name = N'UserId'

Settings.UpdateColumn = delegate (Column column, Table table, List<EnumDefinition> enumDefinitions)
{
    // Access all three extended properties
    if (column.ExtendedProperties.ContainsKey("JsonPropertyName"))
        column.Attributes.Add($"[JsonPropertyName(\"{column.ExtendedProperties["JsonPropertyName"]}\")]");
    
    if (column.ExtendedProperties.ContainsKey("Validator"))
    {
        var validators = column.ExtendedProperties["Validator"].Split('|');
        foreach (var validator in validators)
            column.Attributes.Add($"[{validator}]");
    }
    
    if (column.ExtendedProperties.ContainsKey("Description"))
        column.SummaryComments = column.ExtendedProperties["Description"];
};

Notes

• Extended property names are case-insensitive (using StringComparer.OrdinalIgnoreCase)
• If a database doesn't support named extended properties, a placeholder name is used
• The DatabaseReader.ReadExtendedProperties() method safely handles missing property name columns
• Property names are trimmed of whitespace

What Was Changed

1. RawExtendedProperty Class

• Added PropertyName field to store the extended property name
• Updated constructor signature to accept property name parameter

2. Column Class

• Added ExtendedProperties dictionary: Dictionary<string, string> (case-insensitive)
• Maintains backward compatibility with existing ExtendedProperty string field

3. DatabaseReader

• Updated ReadExtendedProperties() method to read property names from query results
• Added safe fallback when property name column doesn't exist

4. Database-Specific Readers

• SQL Server: Updated query to include ep.name AS [propertyname]
• PostgreSQL: Added placeholder 'Comment' AS "propertyname" (PostgreSQL uses generic comments)
• SQL Server CE: Added placeholder 'ExtendedProperty' AS [propertyname]
• MySQL, Oracle, SQLite: No changes (don't support extended properties)

5. Generator

• Updated AddExtendedPropertiesToFilters() to populate the ExtendedProperties dictionary
• Maintains backward compatibility with existing ExtendedProperty string

6. Settings.cs

• Added example usage in UpdateColumn comments showing how to use the new feature