Chain v4.3

Version 4.3

Updated dependency to Anchor 4.1.

Features

#88 Simple Aggregators

The "simple aggregators" agument the AsCount method. Each returns a single value for the desired column.

• AsAverage(columnName)
• AsMax(columnName)
• AsMin(columnName)
• AsSum(columnName, distinct)

These all return a ScalarDbCommandBuilder with which the caller can specify the return type. They are built on the AggregateColumn model, which overrides the usual column selection process.

For more complex aggregation, use the AsAggregate method. This accepts a collection of AggregateColumn objects, which can be used for both aggregegate functions and grouping.

The original AsCount methods were reworked to fit into this model.

#89 Declarative Aggregators

Attributes can now be used to declare aggregations directly in a model.

[Table("Sales.EmployeeSalesView"]
public class SalesFigures
{
	[AggregateColumn(AggregateType.Min, "TotalPrice")]
	public decimal SmallestSale { get; set; }

	[AggregateColumn(AggregateType.Max, "TotalPrice")]
	public decimal LargestSale { get; set; }

	[AggregateColumn(AggregateType.Average, "TotalPrice")]
	public decimal AverageSale { get; set; }

	[CustomAggregateColumn("Max(TotalPrice) - Min(TotalPrice)")]
	public decimal Range { get; set; }

	[GroupByColumn]
	public int EmployeeKey { get; set; }

	[GroupByColumn]
	public string EmployeeName { get; set; }
}

To use this feature, you need use either of these patterns:

datasource.FromTable(tableName, filter).ToAggregate<TObject>().ToCollection().Execute();
datasource.FromTable<TObject>(filter).ToAggregate().ToCollection().Execute();

In the second version, the table or view name is extracted from the class.

#92 ToObjectStream

Previously, Chain would fully manage database connections by default. Specifically, it would open and close connections automatically unless a transaction was involved. In that case, the developer only needed to manage the transactional data source itself.

However, there are times when a result set is too large to handle at one time. In this case the developer will want an IEnumerable or IAsyncEnumerable instead of a collection. To support this, the ToObjectStream materializer was created.

When used in place of ToCollection, the caller gets a ObjectStream object. This object implements IEnumerable<TObject>, IDisposable, IAsyncDisposable, abd IAsyncEnumerable<TObject>. (That latter two are only available in .NET 6 or later.)

This object stream may be used directly, as shown below, or attached to an RX Observable or TPL Dataflow just like any other enumerable data structure.

//sync pattern

using var objectStream = dataSource.From<Employee>(new { Title = uniqueKey }).ToObjectStream<Employee>().Execute();
foreach (var item in objectStream)
{
	Assert.AreEqual(uniqueKey, item.Title);
}

//async pattern

await using var objectStream = await dataSource.From<Employee>(new { Title = uniqueKey }).ToObjectStream<Employee>().ExecuteAsync();
await foreach (var item in objectStream)
{
	Assert.AreEqual(uniqueKey, item.Title);
}

It is vital that the object stream is disposed after use. If that doesn't occur, the database can suffer from thread exhaustion or deadlocks.

#98 Dynamic Materializers and Desired Columns

Allow the use of WithProperties or ExcludeProperties to be used with...

• .ToDynamicObject
• .ToDynamicObjectOrNull
• .ToDynamicCollection

Bugs

#490 Command Timeout is not being honored in PostgreSQL and MySQL

See the ticket for an explaination for why this was broken.

Technical Debt

#488 Add IAsyncDisposable support

Added support for IAsyncDisposable to transactional data sources.