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Changelog

All notable changes to JetDatabaseReader are documented here. This project follows Semantic Versioning.

[2.2.0] — 2026-04-01

⚠️ Breaking Changes

Area Before After
TableResult.Rows List<List<string>> — string rows List<object[]> — typed CLR rows
ReadTable(string, int) Returned string rows in Rows Now returns typed rows in Rows
ReadTable(string, int, bool) Bool flag selecting typed vs string mode Removed — use ReadTable (typed) or ReadTableAsStrings (strings)
ReadTableAsync(string, int, bool) Async counterpart of removed overload Removed
FirstTableResult Extended TableResult Now extends StringTableResult

✨ New Type: StringTableResult

Dedicated result class for string-mode reads, returned by ReadTableAsStrings. Mirrors TableResult but Rows is List<List<string>>.

Property Type Description
Headers List<string> Column names
Rows List<List<string>> String rows
Schema List<TableColumn> Per-column schema
TableName string Source table name
RowCount int Computed row count
ToDataTable() DataTable All columns typeof(string)

✨ New Methods

Method Returns Description
ReadTableAsStrings(string, int) StringTableResult Sampled string-mode read
ReadTableAsStringsAsync(string, int) Task<StringTableResult> Async variant
TableResult.ToDataTable() DataTable Convert typed result — column types from Schema
StringTableResult.ToDataTable() DataTable Convert string result — all columns typeof(string)

🔧 Improvements & Bug Fixes

  • ACCDB encryption false positive fixed — The Jet4 encryption flag at offset 0x62 is now only checked for ver == 1 (Access 2000–2003 .mdb). Access 2007+ format databases (ver >= 2) set unrelated bits at that offset and were incorrectly rejected with NotSupportedException. All .accdb files and .mdb files saved in Access 2007–2019 format are now readable.
  • Model files split — ColumnSizeUnit, ColumnSize, and TableColumn each have their own .cs file.

📦 Migration Guide

// ── ReadTable — Rows is now typed ─────────────────────────────────────
// Before (v2.1): string rows in Rows
TableResult r = reader.ReadTable("Orders", 10);
string val = r.Rows[0][2];                 // List<List<string>>

// After (v2.2): typed rows in Rows
TableResult r = reader.ReadTable("Orders", 10);
object val = r.Rows[0][2];                 // List<object[]>

// ── ReadTableAsStrings — dedicated string API ─────────────────────────
StringTableResult sr = reader.ReadTableAsStrings("Orders", 10);
string val = sr.Rows[0][2];                // List<List<string>>

// ── bool overload removed ─────────────────────────────────────────────
// Before ❌
TableResult r = reader.ReadTable("Orders", 10, typedValues: true);
// After ✅
TableResult        r  = reader.ReadTable("Orders", 10);
StringTableResult  sr = reader.ReadTableAsStrings("Orders", 10);

// ── ToDataTable ───────────────────────────────────────────────────────
DataTable typed   = reader.ReadTable("Orders", 100).ToDataTable();
DataTable strings = reader.ReadTableAsStrings("Orders", 100).ToDataTable();

[2.1.0] — 2026-03-30

⚠️ Breaking Changes

Area Before After
TableColumn.TypeName string — e.g. "Long Integer" Removed — replaced by Type (System.Type)
TableColumn.SizeDesc string — e.g. "4 bytes" Removed — replaced by Size (ColumnSize struct)
ReadFirstTable() Returned TableResult Now returns FirstTableResult (subclass of TableResult)
GetTableStats() Returned List<(string Name, long RowCount, int ColumnCount)> Now returns List<TableStat>

✨ New Types

Type Description
ColumnSizeUnit Enum: Bits, Bytes, Chars, Variable, Lval
ColumnSize Readonly struct — Value (int?) + Unit (ColumnSizeUnit). Factory methods: FromBits, FromBytes, FromChars. Sentinels: Variable, Lval. ToString() produces a human-readable description.
FirstTableResult Extends TableResult with TableCount (int) — the total number of user tables in the database. Returned by ReadFirstTable().
TableStat Named class with Name (string), RowCount (long), ColumnCount (int). Returned as element of List<TableStat> from GetTableStats().

🔧 Improvements

  • TableResult gains TableName (string) — the table this result was read from — and RowCount (int) computed property.
  • TableColumn.Type (System.Type) — exact CLR type, consistent with ColumnMetadata.ClrType.
  • TableColumn.Size (ColumnSize) — structured size with programmatic access to numeric value and unit; ToString() preserves the previous human-readable output.

📦 Migration Guide

// ── TableColumn schema properties ────────────────────────────────────
// Before
string typeName = col.TypeName;   // "Long Integer"
string sizeDesc = col.SizeDesc;   // "4 bytes"
// After
Type   clrType  = col.Type;                    // typeof(int)
int?   bytes    = col.Size.Value;              // 4
string display  = col.Size.ToString();         // "4 bytes"
bool   isVar    = col.Size.Unit == ColumnSizeUnit.Variable;

// ── ReadFirstTable ────────────────────────────────────────────────────
// Before
TableResult      r = reader.ReadFirstTable();
// After
FirstTableResult r = reader.ReadFirstTable();
int total = r.TableCount;   // new property on FirstTableResult

// ── GetTableStats ─────────────────────────────────────────────────────
// Before — tuple list
foreach (var (name, rows, cols) in reader.GetTableStats()) { ... }
// After — named class
foreach (TableStat s in reader.GetTableStats())
    Console.WriteLine($"{s.Name}: {s.RowCount} rows, {s.ColumnCount} cols");

[2.0.1] — 2026-03-29

⚠️ Breaking Changes

Before After Notes
TablePreviewResult TableResult Renamed for clarity — remove the Preview prefix
TablePreviewColumn TableColumn Renamed for clarity — remove the Preview prefix

📦 Migration Guide

// Before
TablePreviewResult p = r.ReadTable("Orders", 10);
foreach (TablePreviewColumn col in p.Schema)
    Console.WriteLine($"{col.Name}: {col.TypeName} ({col.SizeDesc})");

// After
TableResult p = r.ReadTable("Orders", 10);
foreach (TableColumn col in p.Schema)
    Console.WriteLine($"{col.Name}: {col.TypeName} ({col.SizeDesc})");

[2.0.0] — 2026-03-28

⚠️ Breaking Changes

Area v1 behaviour v2 behaviour
Constructor new JetDatabaseReader(path) AccessReader.Open(path) — factory method required
ReadTable() Returned (headers, rows, schema) tuple Now an overload — ReadTable(string, int) returns TableResult
ReadTableAsDataTable() Returned DataTable with string columns Renamed to ReadTableAsStringDataTable()
StreamRows() Returned IEnumerable<string[]> Now returns IEnumerable<object[]> with native CLR types
ReadAllTables() Returned DataTable with string columns Now returns DataTable with typed CLR columns
ReadAllTablesAsync() Same string behaviour Now returns typed CLR columns

✨ New Methods

Method Description
ReadTable() Primary read method — typed DataTable (replaces ReadTableAsDataTableTyped)
ReadTable(string, int) Sampled-rows overload — returns TablePreviewResult (headers, rows, schema)
ReadTableAsync() Async typed DataTable
ReadTableAsync(string, int) Async sampled-rows overload — returns Task<TablePreviewResult>
StreamRowsAsStrings() Compatibility streaming — IEnumerable<string[]>
ReadAllTablesAsStrings() Bulk read with string columns
ReadAllTablesAsStringsAsync() Async bulk read with string columns
TableQuery.Where(Func<object[], bool>) Typed row predicate
TableQuery.WhereAsStrings(Func<string[], bool>) String row predicate
TableQuery.Execute() Returns IEnumerable<object[]>
TableQuery.ExecuteAsStrings() Returns IEnumerable<string[]>
TableQuery.FirstOrDefault() Returns first object[] or null
TableQuery.FirstOrDefaultAsStrings() Returns first string[] or null
TableQuery.Count() / CountAsStrings() Count per chain
GetColumnMetadata() Rich per-column metadata with CLR type
GetStatistics() / GetStatisticsAsync() Database-level statistics + cache hit rate
TablePreviewResult Result type for sampled-rows overload — Headers, Rows, Schema
TablePreviewColumn Schema entry — Name, TypeName (string), SizeDesc (string)

🔧 Improvements

  • FileShare default changed to FileShare.Read — other processes may read but not write while the database is open; pass FileShare.ReadWrite explicitly when Microsoft Access has the file open
  • LRU page cache (256-page default, ~1 MB for Jet4 pages)
  • Parallel page reads option (ParallelPageReadsEnabled)
  • AccessReaderOptions configuration object (PageCacheSize, FileAccess, FileShare, ValidateOnOpen)
  • DatabaseStatistics and ColumnMetadata types
  • IAccessReader interface — fully testable and mockable
  • Full XML documentation on all public members

📦 Migration Guide

// ── Open ────────────────────────────────────────────────────────────
// v1
using var r = new JetDatabaseReader("db.mdb");
// v2
using var r = AccessReader.Open("db.mdb");

// ── Read typed DataTable ─────────────────────────────────────────────
// v1 — no equivalent (all columns were strings)
// v2
DataTable dt = r.ReadTable("Orders");
int id = (int)dt.Rows[0]["OrderID"];

// ── Read string DataTable (compatibility) ────────────────────────────
// v1
DataTable dt = r.ReadTableAsDataTable("Orders");
// v2
DataTable dt = r.ReadTableAsStringDataTable("Orders");

// ── Sample with schema ──────────────────────────────────────────────
// v1
var (h, rows, schema) = r.ReadTable("Orders", maxRows: 10);
// v2
TablePreviewResult p = r.ReadTable("Orders", 10);
// p.Headers / p.Rows / p.Schema[i].Name, .TypeName, .SizeDesc

// ── Stream rows (typed) ──────────────────────────────────────────────
// v1
foreach (string[] row in r.StreamRows("Orders")) { ... }
// v2 — typed
foreach (object[] row in r.StreamRows("Orders")) { int id = (int)row[0]; }
// v2 — compat
foreach (string[] row in r.StreamRowsAsStrings("Orders")) { ... }

// ── Bulk read ────────────────────────────────────────────────────────
// v1 — returned string columns
var tables = r.ReadAllTables();
// v2 — returns typed columns
var tables = r.ReadAllTables();
// v2 — compat strings
var tables = r.ReadAllTablesAsStrings();

[1.0.0] — 2026-03-27

  • Pure-managed JET3/Jet4 reader (no OleDB/ODBC/ACE)
  • All standard column types (Text, Integer, Currency, GUID, MEMO, OLE)
  • Multi-page LVAL chain support
  • OLE Object magic-byte detection (JPEG, PNG, PDF, ZIP, DOC, RTF)
  • Compressed Unicode (Jet4) decoding
  • Code page auto-detection (non-Western text)
  • Encryption detection (NotSupportedException)
  • Streaming API (StreamRows)
  • IProgress<int> callbacks
  • 256-page LRU cache