[jogibear9988]

Add an explicit immutable Filter<T> alternative to the lambda API in #206. Callers identify DTO properties with typed selectors and compose named comparison operations.

Public API

The Select<T> extension and Filter<T> are in DotNetProjects.Migrator.Framework. Public signatures:

public static IReadOnlyList<T> Select<T>(
    this ITransformationProvider provider,
    string table,
    Filter<T> filter)
    where T : class, new();

// Filter<T> is immutable and requires T : class, new().
public static Filter<T> Equal<TValue>(
    Expression<Func<T, TValue>> column, TValue value);
public static Filter<T> NotEqual<TValue>(
    Expression<Func<T, TValue>> column, TValue value);
public static Filter<T> LessThan<TValue>(
    Expression<Func<T, TValue>> column, TValue value);
public static Filter<T> LessThanOrEqual<TValue>(
    Expression<Func<T, TValue>> column, TValue value);
public static Filter<T> GreaterThan<TValue>(
    Expression<Func<T, TValue>> column, TValue value);
public static Filter<T> GreaterThanOrEqual<TValue>(
    Expression<Func<T, TValue>> column, TValue value);
public static Filter<T> IsNull<TValue>(
    Expression<Func<T, TValue>> column);
public static Filter<T> IsNotNull<TValue>(
    Expression<Func<T, TValue>> column);

public Filter<T> And(Filter<T> other);
public Filter<T> Or(Filter<T> other);
public Filter<T> Not();

DTO used in the examples

using DotNetProjects.Migrator.Framework;
using DtoColumn = System.ComponentModel.DataAnnotations.Schema.ColumnAttribute;

public sealed class ScreenDto
{
    public int Id { get; set; }
    public bool Archive { get; set; }

    [DtoColumn("GenericDefinition")]
    public string Definition { get; set; }
}

This uses the DTO mapping introduced in #206, including inherited properties and standard column/not-mapped attributes.

Usage

Assuming provider is the migration's ITransformationProvider:

var minimumId = 10;

// Type-safe property selectors and comparison values.
var filter = Filter<ScreenDto>.Equal(x => x.Archive, false)
    .And(Filter<ScreenDto>.GreaterThan(x => x.Id, minimumId));

IReadOnlyList<ScreenDto> screens =
    provider.Select<ScreenDto>("Common_Screens", filter);

// T can also be inferred from Filter<ScreenDto>.
var sameScreens = provider.Select("Common_Screens", filter);

// Grouped OR, with explicit inclusion of NULL rows.
var otherDefinitions = Filter<ScreenDto>.IsNull(x => x.Definition)
    .Or(Filter<ScreenDto>.NotEqual(x => x.Definition, "obsolete"));

var activeOtherScreens = provider.Select(
    "Common_Screens",
    Filter<ScreenDto>.Equal(x => x.Archive, false)
        .And(otherDefinitions));

// Negation creates a new filter.
var archivedScreens = provider.Select(
    "Common_Screens",
    Filter<ScreenDto>.Equal(x => x.Archive, false).Not());

// Filters can be reused. Composition never modifies the original.
var aboveMinimum = Filter<ScreenDto>.GreaterThan(x => x.Id, minimumId);
var activeAboveMinimum = aboveMinimum.And(
    Filter<ScreenDto>.Equal(x => x.Archive, false));

Inside a Classic migration, use Database.Select<ScreenDto>(table, filter); in a FluentMigration, use Context.Select<ScreenDto>(table, filter). Reads execute immediately and return materialized DTOs.

Supported behavior and limits

• TValue connects the selected property type to the comparison value type. Selectors must name direct mapped properties in their declared type; casts, calculations, nested properties and widened/boxed selectors are rejected.
• Filters capture values when built. Changing a local variable later does not change an existing filter. And, Or and Not return new immutable filters and preserve grouping.
• Null checks require nullable value or reference properties. Ordering on strings, booleans, GUIDs and enums, and byte-array comparisons, are unsupported.
• Both APIs share DTO mapping, quoting, native parameter binding, SQL null/collation semantics, transactions and command/reader disposal with Add typed DTO selection, updates and deletes #206.
• A null filter throws; use Select<T>(table) to read all rows.

Part 2 of the implementation for #202. Depends on #206; merge #206 first, then retarget this PR to master. The current base is codex/dto-select-predicates, so this diff contains only the builder additions.

Validation:

• Solution build passed.
• 877 unit tests and 489 SQLite tests passed; 27 builder tests cover composition, immutable reuse, null semantics, parameter safety, transactions and invalid selectors.
• Oracle/HANA/Informix binding tests now exercise both APIs; the native-driver integration fixture exercises both APIs across the existing eleven-database CI matrix.
• Documentation tests/link checks passed; all 110 published C# examples compiled and 8 SQLite parity checks passed.
• Non-SQLite live databases were not run locally.

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