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Add QueryCells to read cell formulas, font colors and number formats - #1020

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@virzak virzak commented Oct 10, 2026 •

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Part of #239

Row queries return only cached values, so callers can't tell whether a value came from a formula, and cell styling is lost. This adds QueryCells/QueryCellsAsync, which yields each stored cell with its formula, font color and number format. Existing queries are unchanged.

await foreach (var cell in importer.QueryCellsAsync(stream, "Sheet1"))
{
    // cell.Reference, RowIndex, ColumnIndex, Value
    // cell.HasFormula, cell.Formula
    // cell.FontColor?.Rgb / Theme / Tint / Indexed / Auto
    // cell.NumberFormat, e.g. "0.0%", or null for General
}
  • Cells that are part of a shared formula report HasFormula = true with Formula = null, since only the anchor cell stores the text.
  • FontColor is a new ExcelColor rather than the System.Drawing.Color used by OpenXmlCellStyle (Add deferred cell style updates #1013), because theme colors and tints can't be represented without resolving the theme.

Tested against a workbook saved by Excel 16 with shared formulas, theme colors with tints and custom number formats.

Summary by CodeRabbit

  • New Features

    • Added asynchronous worksheet cell queries that return cell references, values, formulas, font colors, and number formats.
    • Supports reading workbooks from file paths or streams, selecting sheets by name, cancellation, and optional stream preservation.
    • Includes support for RGB, theme, indexed, and automatic font colors.
    • Invalid cell references are reported clearly.
  • Documentation

    • Added usage guidance and examples for querying cells with metadata.

Row queries drop whether a value came from a formula and how the cell is
styled, which callers need when importing hand-edited sheets.
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No actionable comments were generated in the recent review. 🎉

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Reviewing files that changed from the base of the PR and between 3544f39 and 009e79d.

📒 Files selected for processing: 6
  • README_V2.md
  • benchmarks/MiniExcel.Benchmarks/BenchmarkSections/QueryExcelBenchmark.cs
  • src/MiniExcel.OpenXml/Api/OpenXmlImporter.cs
  • src/MiniExcel.OpenXml/Reader/OpenXmlReader.Cells.cs
  • tests/MiniExcel.OpenXml.Tests/Cells/QueryCellsWithMetadataAsyncTests.cs
  • tests/MiniExcel.OpenXml.Tests/Cells/QueryCellsWithMetadataTests.cs

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📝 Walkthrough

Adds asynchronous worksheet cell queries that return values, formulas, font colors, and number formats. The change includes cell parsing, importer overloads, tests, documentation, and a benchmark.

Changes: Worksheet cell metadata

Layer / File(s) Summary
Cell and style metadata
src/MiniExcel.OpenXml/Models/ExcelCell.cs, src/MiniExcel.OpenXml/Styles/OpenXmlStyles.cs
Adds ExcelCell and ExcelColor. Style parsing records font IDs and font colors, and provides font-color lookup by cell style.
Worksheet cell parsing
src/MiniExcel.OpenXml/Reader/OpenXmlReader.Cells.cs, src/MiniExcel.OpenXml/Reader/OpenXmlReader.cs
Adds asynchronous worksheet cell enumeration and parsing for references, formulas, values, and style metadata. Validates row and column bounds. Also renames the relationship namespace array and makes the cell-type argument nullable.
Importer API and validation
src/MiniExcel.OpenXml/Api/OpenXmlImporter.cs, tests/MiniExcel.OpenXml.Tests/Cells/*, README_V2.md, benchmarks/MiniExcel.Benchmarks/BenchmarkSections/QueryExcelBenchmark.cs
Adds path- and stream-based asynchronous query overloads. Tests cover returned metadata and invalid references. Documentation describes metadata queries, and a benchmark enumerates queried cells.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant Caller
  participant OpenXmlImporter
  participant OpenXmlReader
  participant OpenXmlStyles
  Caller->>OpenXmlImporter: QueryCellsWithMetadataAsync(path or stream)
  OpenXmlImporter->>OpenXmlReader: Enumerate cells from selected worksheet
  OpenXmlReader->>OpenXmlStyles: Get font color for cell style
  OpenXmlStyles-->>OpenXmlReader: Return font color
  OpenXmlReader-->>OpenXmlImporter: Yield ExcelCell
  OpenXmlImporter-->>Caller: Yield ExcelCell
Loading

Suggested reviewers: michelebastione

Merge Risk: ⚪ Minimal · up to 009e7

QueryCellsWithMetadata adds new read-only APIs and leaves existing queries unchanged. No concrete merge-blocking defect remains after review.

Security architecture risk: 🔵 Low · up to 009e7

The new read-only API reuses existing archive and XML controls and returns formula text without executing it. Additional workbook-controlled metadata is retained in memory; resource limits and exposure through consuming applications were not established.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

  • inferred — The inspected input-processing scope is the supplied workbook and the caller's process resources. No additional service identity or cross-tenant authority appears in this call path. Whether applications expose it to untrusted uploads or share a worker across tenants remains unknown.

Trust Boundaries and Controls

  • observed — Formula contents are returned as text rather than evaluated. Worksheet relationship targets are matched against entries in the supplied archive, and XML readers use XmlResolver = null. These controls constrain the inspected parser path without establishing safety for downstream uses of returned strings.

Hardening Proposals

  • proposed — For deployments accepting hostile workbooks, consider an aggregate parsing budget covering decompressed content and retained metadata, including fonts, alongside worker memory isolation. This is a hardening proposal, not a verified vulnerability finding.
Pre-merge checks: Passed 4 · Failed 1

Failed Failed checks: 1 warning

Check name Status Explanation Resolution
Docstring Coverage Warning Docstring coverage is 7.89% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 38 functions across 10 files. (1 skipped: … Write docstrings for the functions missing them to satisfy the coverage threshold.
Passed Passed checks: 4 passed
Check name Status Explanation
Description Check Passed Check skipped - CodeRabbit’s high-level summary is enabled.
Title check Passed The title clearly describes the primary change: adding cell queries that expose formulas, font colors, and number formats. The implementation uses the more specific API name QueryCellsWithMetadata, bu…
Linked Issues check Passed Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check Passed Check skipped because no linked issues were found for this pull request.
Full details: Title check

Explanation

The title clearly describes the primary change: adding cell queries that expose formulas, font colors, and number formats. The implementation uses the more specific API name QueryCellsWithMetadata, but the title remains accurate and concise.

Full details: Docstring Coverage

Explanation

Docstring coverage is 7.89% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 38 functions across 10 files. (1 skipped: 1 unsupported.)

Resolution

Write docstrings for the functions missing them to satisfy the coverage threshold.

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@virzak virzak changed the title Add QueryCells to read cell formulas and font colors Add QueryCells to read cell formulas, font colors and number formats Oct 11, 2026
@virzak
virzak marked this pull request as ready for review October 11, 2026 11:48

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Caution

Some comments are outside the diff and can’t be posted inline due to GitHub limitations.

⚠️ Outside diff range comments (1)

🟡 Minor · Reject an explicit out-of-range cell reference before inferring a… · OpenXmlReader.Cells.cs:90-98

src/MiniExcel.OpenXml/Reader/OpenXmlReader.Cells.cs:90-98
🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win

Reject an explicit out-of-range cell reference before inferring a column.

TryParseCellReference rejects XFE1 after setting referenceColumn above the worksheet limit. The current fallback then uses nextColumnNumber, so QueryCellsAsync can return the value with a different Reference and ColumnIndex. Match the existing reader behavior and reject the explicit invalid reference.

Suggested fix
         if (CellReferenceConverter.TryParseCellReference(aR, out var referenceColumn, out _))
         {
             columnNumber = referenceColumn;
         }
+        else if (!string.IsNullOrEmpty(aR) && referenceColumn > CellReferenceConverter.MaxColumnNumber)
+        {
+            throw new InvalidDataException($"Cell reference '{aR}' is invalid.");
+        }
         else if (columnNumber > CellReferenceConverter.MaxColumnNumber)
         {
             throw new InvalidDataException("The worksheet contains more columns than Excel supports.");
         }
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Review comment at @src/MiniExcel.OpenXml/Reader/OpenXmlReader.Cells.cs around
lines 90 - 98:
Update the column-selection logic in QueryCellsAsync so a nonempty explicit cell
reference rejected by CellReferenceConverter.TryParseCellReference is also
rejected when referenceColumn exceeds MaxColumnNumber, rather than falling back
to nextColumnNumber. Preserve the existing inferred-column overflow check for
missing or otherwise non-out-of-range references.

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Outside diff comments:
Review comments at @src/MiniExcel.OpenXml/Reader/OpenXmlReader.Cells.cs:
- Around line 90-98: Update the column-selection logic in QueryCellsAsync so a
nonempty explicit cell reference rejected by
CellReferenceConverter.TryParseCellReference is also rejected when
referenceColumn exceeds MaxColumnNumber, rather than falling back to
nextColumnNumber. Preserve the existing inferred-column overflow check for
missing or otherwise non-out-of-range references.

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Actionable comments posted: 1


  • 🪄 Fix CodeRabbit comments on this PR
🤖 Prompt to fix review comments
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only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
Review comments at @src/MiniExcel.OpenXml/Reader/OpenXmlReader.Cells.cs:
- Around line 95-98: Update the cell-reference validation branch so every
nonempty aR that fails TryParseCellReference is rejected with
InvalidDataException, regardless of referenceColumn. Keep sequential-column
fallback only when aR is missing.

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  • src/MiniExcel.OpenXml/Reader/OpenXmlReader.Cells.cs
  • tests/MiniExcel.OpenXml.Tests/Cells/QueryCellsAsyncTests.cs

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Comment thread src/MiniExcel.OpenXml/Reader/OpenXmlReader.Cells.cs
@michelebastione

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Hello @virzak, thank you for contributing again! I'll have a look at these as soon as I can.

virzak and others added 4 commits October 14, 2026 09:51
Building the string for every cell made QueryCells several times slower
on large sheets.
QueryCells returns one per cell, so a class cost an allocation per cell.
Fixed a typo and a newline, and slightly adjusted the new tests
/// Cells are returned in document order, one <see cref="ExcelCell"/> per cell element in the file, so cells that were never written are skipped.
/// </remarks>
[CreateSyncVersion]
public async IAsyncEnumerable<ExcelCell> QueryCellsAsync(Stream stream, string? sheetName = null, bool leaveOpen = false, [EnumeratorCancellation] CancellationToken cancellationToken = default)

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@virzak I'm not sure the name QueryCells accurately conveys the purpose of the method. Although the summary clarifies it I think as an API method it should be renamed to something less ambiguous, like QueryCellsMetadata or similar.

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@michelebastione would QueryCellsWithMetadata work?

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Sorry for the late reply. It doesn't quite roll of the tongue but it is unambiguous. Feel free to suggest other ones, otherwise proceed.

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Renamed to QueryCellsWithMetadata in 009e79d.

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