connect-pbid

name	connect-pbid
version	26.2
description	TOM and ADOMD.NET guidance via PowerShell for connecting to Power BI Desktop's local Analysis Services instance. Covers model enumeration, DAX queries, metadata modification, annotations, calendar definitions, field parameters, query tracing, and DAX library package management (daxlib.org). Automatically invoke when the user mentions "Power BI Desktop", "Analysis Services port", "TOM", "ADOMD", "daxlib", "DAX library", "DAX UDF package", or asks to "connect to PBI Desktop", "query PBI Desktop with DAX", "modify PBI Desktop model", "add a measure to PBI", "capture visual queries", "create a field parameter", "validate DAX", "intercept DAX queries", "install daxlib", "add DAX SVG", "add IBCS".

Connect to Power BI Desktop (Local Analysis Services)

CRITICAL: Record mistakes, surprises, and model-specific nuances encountered while using this skill in .claude/rules/connect-pbid.md. This file must begin with "Learnings from Claude about connecting to semantic models via the connect-pbid skill". Write only active reference notes (e.g. "QueryGroup property returns an object; access .Folder for the name string"); do not log a changelog or history of events. Omit anything already documented in the skill or its references. Keep the file under 1500 characters at all times; prune stale entries when adding new ones. Do not over-attend to this file; update it only when something genuinely unexpected is discovered.

Note: No MCP server required; do not use this skill with MCP servers or CLI tools. Use this skill to execute PowerShell commands directly via Bash to connect to Power BI Desktop's local Analysis Services instance.

Expert guidance for connecting to Power BI Desktop's local tabular model via the Tabular Object Model (TOM) and ADOMD.NET in PowerShell. Covers connection, enumeration, DAX queries, query traces, and full model modification.

When to Use This Skill

Activate only when the Tabular Editor CLI or a Power BI MCP server is unavailable. TOM is more reliable than direct TMDL editing because it validates changes against the engine and applies them atomically.

WARNING: This skill does NOT support remote models via the XMLA endpoint. For Direct Lake models or models hosted in Fabric, use the Tabular Editor CLI or a Power BI MCP server instead; the local Analysis Services proxy does not expose Direct Lake databases to external TOM/ADOMD.NET connections.

Critical

• Power BI Desktop must be open with a model loaded before connecting; if there are errors it is likely due to a "thin report" connected to a remote model, or a Direct Lake model (which uses a remote proxy that blocks external connections)
• The local Analysis Services instance only accepts connections from localhost
• Multiple PBI Desktop files open means multiple msmdsrv.exe processes on different ports. Connect to each port, read $server.Databases[0].Name, and ask the user which model to work with if more than one is found
• Always use a timeout of 60000ms or higher for PowerShell commands via Bash
• Shell escaping: Bash eats PowerShell $ variables ($env:TEMP, $server, etc.) silently. Two options: (1) single-quote the -Command arg so Bash passes $ literally to PowerShell; (2) write a .ps1 file with a heredoc (single-quoted delimiter preserves $) and use -File. On macOS via Parallels, the prlctl -> cmd.exe -> powershell.exe chain adds extra escaping layers; .ps1 files are more reliable for complex scripts but inline -Command with single quotes works for short commands.
• Always use -ExecutionPolicy Bypass when running PowerShell commands or scripts. Windows blocks unsigned scripts by default.
• Script file location -- persistent scripts should go in the agent harness's scripts directory for the project (.claude/scripts/, .github/scripts/, .cursor/scripts/, .gemini/scripts/, etc. depending on the harness). Ephemeral or throwaway scripts should go in a project tmp/ directory (which should be .gitignored). Do not write scripts to ./ root or /tmp/.
• Do not modify model metadata without explicit user direction
• Always call $model.SaveChanges() to persist modifications; without it, changes are discarded
• For macOS users running PBI Desktop in Parallels, see parallels-macos.md
• Validation hooks are active for this plugin; they validate DAX references, enforce measure metadata, check referential integrity, and report compatibility level upgrade opportunities. Toggle checks in hooks/config.yaml.

1. Prerequisites

Requirement	Description
Power BI Desktop	Open with a model loaded (.pbix or .pbip)
PowerShell	Available on the machine running PBI Desktop
NuGet CLI	For package installation (winget install Microsoft.NuGet)
TOM NuGet Package	Microsoft.AnalysisServices.retail.amd64 -- model metadata
ADOMD.NET Package	Microsoft.AnalysisServices.AdomdClient.retail.amd64 -- DAX queries

Install both packages only if not already present:

$pkgDir = "$env:TEMP\tom_nuget"
if (-not (Test-Path "$pkgDir\Microsoft.AnalysisServices.retail.amd64")) {
    nuget install Microsoft.AnalysisServices.retail.amd64 -OutputDirectory $pkgDir -ExcludeVersion
}
if (-not (Test-Path "$pkgDir\Microsoft.AnalysisServices.AdomdClient.retail.amd64")) {
    nuget install Microsoft.AnalysisServices.AdomdClient.retail.amd64 -OutputDirectory $pkgDir -ExcludeVersion
}

Packages install DLLs under lib\net45\. Load with Add-Type -Path.

If a TOM operation fails with a compatibility level error or missing type, the .retail.amd64 package may be too old. A newer package (Microsoft.AnalysisServices, .NET 8+) ships with more recent TOM features. See daxlib.md for details on package differences.

2. Quickstart

Find the port, load TOM, connect, enumerate -- in one script:

# Find port
$pids = (Get-Process msmdsrv -ErrorAction SilentlyContinue).Id
$ports = netstat -ano | Select-String "LISTENING" |
    Where-Object { $pids -contains ($_ -split "\s+")[-1] } |
    ForEach-Object { ($_ -split "\s+")[2] -replace ".*:" }

# Load TOM
$basePath = "$env:TEMP\tom_nuget\Microsoft.AnalysisServices.retail.amd64\lib\net45"
Add-Type -Path "$basePath\Microsoft.AnalysisServices.Core.dll"
Add-Type -Path "$basePath\Microsoft.AnalysisServices.Tabular.dll"

# Connect to first port
$server = New-Object Microsoft.AnalysisServices.Tabular.Server
$server.Connect("Data Source=localhost:$($ports[0])")
$model = $server.Databases[0].Model

# Enumerate
foreach ($table in $model.Tables) {
    Write-Output "TABLE: [$($table.Name)] ($($table.Columns.Count) cols, $($table.Measures.Count) measures)"
}
Write-Output "Relationships: $($model.Relationships.Count)"

$server.Disconnect()

Port discovery methods:

Method	Install Type	Command
Port file	Non-Store PBI Desktop	Get-Content "$env:LOCALAPPDATA\Microsoft\Power BI Desktop\AnalysisServicesWorkspaces\*\Data\msmdsrv.port.txt"
Port file	Store PBI Desktop	Get-Content "$env:LOCALAPPDATA\Packages\Microsoft.MicrosoftPowerBIDesktop_*\LocalState\AnalysisServicesWorkspaces\*\Data\msmdsrv.port.txt"
netstat	Any	netstat -ano | findstr LISTENING | findstr <PID>

3. Loading TOM, Connecting, and Saving Changes

Load Assemblies

$basePath = "$env:TEMP\tom_nuget\Microsoft.AnalysisServices.retail.amd64\lib\net45"
Add-Type -Path "$basePath\Microsoft.AnalysisServices.Core.dll"
Add-Type -Path "$basePath\Microsoft.AnalysisServices.Tabular.dll"
Add-Type -Path "$basePath\Microsoft.AnalysisServices.Tabular.Json.dll"

Connect

$server = New-Object Microsoft.AnalysisServices.Tabular.Server
$server.Connect("Data Source=localhost:<PORT>")

# PBI Desktop always has exactly one database
$db = $server.Databases[0]
$model = $db.Model

Save Changes

Only save after all changes are made. After modifications, persist with:

$model.SaveChanges()

Changes appear immediately in PBI Desktop. The user cannot undo with Ctrl+Z in Power BI, which is a disadvantage of this approach.

Disconnect

IMPORTANT: Remember to disconnect after modifications are done. NEVER remain connected, which can lead to orphaned processes.

$server.Disconnect()

Connection Properties

Write-Output "Server: $($server.Name)"
Write-Output "Version: $($server.Version)"
Write-Output "Database: $($db.Name)"
Write-Output "Compatibility: $($db.CompatibilityLevel)"

4. Refreshing the Model

Trigger a data refresh via TMSL (Tabular Model Scripting Language) or TOM's RequestRefresh API. This re-executes Power Query/M expressions and reloads data into the VertiPaq engine.

# Full refresh of a single table via TMSL
$dbName = $server.Databases[0].Name
$tmsl = '{ "refresh": { "type": "full", "objects": [{ "database": "' + $dbName + '", "table": "Sales" }] } }'
$server.Execute($tmsl)

# Or via TOM RequestRefresh API
$model.Tables["Sales"].RequestRefresh([Microsoft.AnalysisServices.Tabular.RefreshType]::Full)
$model.SaveChanges()

Refresh Type	Behaviour
full	Drop data, re-query source, recalculate DAX
calculate	Recalculate DAX only (no source query)
automatic	Engine decides per-partition what's needed
dataOnly	Re-query source but skip DAX recalculation

For detailed examples and all refresh methods, see refresh-model.md.

5. Querying with DAX

Load ADOMD.NET

Add-Type -Path "$env:TEMP\tom_nuget\Microsoft.AnalysisServices.AdomdClient.retail.amd64\lib\net45\Microsoft.AnalysisServices.AdomdClient.dll"

Open a Connection

$conn = New-Object Microsoft.AnalysisServices.AdomdClient.AdomdConnection
$conn.ConnectionString = "Data Source=localhost:<PORT>"
$conn.Open()

Execute a Query

All queries should preferably use SUMMARIZECOLUMNS. Check dax.guide online for information about DAX functions, if necessary.

Important: ADOMD.NET returns fully-qualified column names (e.g., 'Monsters'[Name] not Name). Do not access columns by short name ($reader["Name"]) -- it fails silently and returns blank. Use $reader.GetName($i) to discover column names, then access by index:

$cmd = $conn.CreateCommand()
$cmd.CommandText = "EVALUATE SUMMARIZECOLUMNS('Table'[Column], ""@MeasureName"", [Measure])"

$reader = $cmd.ExecuteReader()

# Always iterate by index and use GetName() to map columns
while ($reader.Read()) {
    for ($i = 0; $i -lt $reader.FieldCount; $i++) {
        Write-Output "$($reader.GetName($i)): $($reader.GetValue($i))"
    }
    Write-Output "---"
}
$reader.Close()

DAX Rules

• Always fully qualify column references with single-quoted table names: 'Sales'[Amount], not [Amount]. This applies everywhere -- measures, calculated columns, queries. Unqualified columns cause ambiguity errors.
• Table names are always single-quoted in DAX: 'Sales'[Amount], 'D&D 5E Monsters'[CR]. Even simple names like Sales should be quoted as 'Sales' for consistency.
• Measure references are the only exception -- they are always unqualified: [Total Revenue]
• String literals in DAX use double quotes, escaped as "" inside PowerShell here-strings

Query Patterns

# Full table scan
$cmd.CommandText = "EVALUATE 'Sales'"

# Filtered with CALCULATETABLE
$cmd.CommandText = "EVALUATE CALCULATETABLE('Sales', 'Sales'[Region] = ""West"")"

# Aggregation
$cmd.CommandText = "EVALUATE SUMMARIZECOLUMNS('Date'[Year], ""@Total"", SUM('Sales'[Amount]))"

# Scalar via ROW
$cmd.CommandText = "EVALUATE ROW(""Result"", COUNTROWS('Sales'))"

# DMV queries (model metadata via SQL-like syntax)
$cmd.CommandText = "SELECT * FROM `$SYSTEM.TMSCHEMA_TABLES"
$cmd.CommandText = "SELECT * FROM `$SYSTEM.TMSCHEMA_MEASURES"
$cmd.CommandText = "SELECT * FROM `$SYSTEM.TMSCHEMA_COLUMNS"
$cmd.CommandText = "SELECT * FROM `$SYSTEM.TMSCHEMA_RELATIONSHIPS"

Close Connection

$conn.Close()

6. Modifying a Semantic Model

All modifications require a TOM connection (section 3). Call $model.SaveChanges() after each batch of changes.

A. CRUD by Object Type

For full CRUD examples of every object type, see tom-object-types.md.

Common object types and their TOM collections (not exhaustive -- see Microsoft TOM API docs for the full namespace):

Object	Collection	Create	Read	Update	Delete
Table	$model.Tables	New-Object ...Table	$model.Tables["Name"]	Set properties	.Remove($obj)
Column	$table.Columns	New-Object ...DataColumn	$table.Columns["Name"]	Set properties	.Remove($obj)
Measure	$table.Measures	New-Object ...Measure	$table.Measures["Name"]	Set properties	.Remove($obj)
Calculated Column	$table.Columns	New-Object ...CalculatedColumn	Filter by type	Set .Expression	.Remove($obj)
Calculated Table	$model.Tables	Table + calculated partition	Check partition type	Set partition expr	.Remove($obj)
Relationship	$model.Relationships	New-Object ...SingleColumnRelationship	Index or filter	Set properties	.Remove($obj)
Hierarchy	$table.Hierarchies	New-Object ...Hierarchy	$table.Hierarchies["Name"]	Modify levels	.Remove($obj)
Role	$model.Roles	New-Object ...ModelRole	$model.Roles["Name"]	Set permissions	.Remove($obj)
Perspective	$model.Perspectives	New-Object ...Perspective	$model.Perspectives["Name"]	Toggle membership	.Remove($obj)
Culture	$model.Cultures	New-Object ...Culture	$model.Cultures["en-US"]	Set translations	.Remove($obj)
Partition	$table.Partitions	New-Object ...Partition	$table.Partitions["Name"]	Set source/expression	.Remove($obj)
Annotation	Any object	$obj.Annotations.Add(...)	$obj.Annotations["Key"]	Set .Value	.Remove($obj)
Expression	$model.Expressions	New-Object ...NamedExpression	$model.Expressions["Name"]	Set .Expression	.Remove($obj)
Data Source	$model.DataSources	New-Object ...StructuredDataSource	$model.DataSources["Name"]	Set connection	.Remove($obj)
Calculation Group	$model.Tables	Table with CalculationGroup	Filter by type	Add/remove items	.Remove($obj)

Quick examples (inline):

# Add a measure
$m = New-Object Microsoft.AnalysisServices.Tabular.Measure
$m.Name = "Total Revenue"
$m.Expression = "SUM(Sales[Amount])"
$m.FormatString = "`$#,0"
$m.Description = "Sum of all sales amounts"
$model.Tables["Sales"].Measures.Add($m)

# Add a relationship
$rel = New-Object Microsoft.AnalysisServices.Tabular.SingleColumnRelationship
$rel.Name = "Sales_to_Date"
$rel.FromColumn = $model.Tables["Sales"].Columns["DateKey"]
$rel.ToColumn = $model.Tables["Date"].Columns["DateKey"]
$rel.FromCardinality = [Microsoft.AnalysisServices.Tabular.RelationshipEndCardinality]::Many
$rel.ToCardinality = [Microsoft.AnalysisServices.Tabular.RelationshipEndCardinality]::One
$model.Relationships.Add($rel)

# Rename a column
$model.Tables["Sales"].Columns["amt"].Name = "Amount"

# Hide a table
$model.Tables["Bridge"].IsHidden = $true

# Delete a measure
$m = $model.Tables["Sales"].Measures["Old Measure"]
$model.Tables["Sales"].Measures.Remove($m)

# Add a role with RLS
$role = New-Object Microsoft.AnalysisServices.Tabular.ModelRole
$role.Name = "Region Filter"
$role.ModelPermission = [Microsoft.AnalysisServices.Tabular.ModelPermission]::Read
$model.Roles.Add($role)
$tp = New-Object Microsoft.AnalysisServices.Tabular.TablePermission
$tp.Table = $model.Tables["Sales"]
$tp.FilterExpression = "[Region] = USERNAME()"
$role.TablePermissions.Add($tp)

$model.SaveChanges()

B. Discovering Object Types, Properties, and Setting Values

For complete TOM object type tables, PowerShell reflection patterns for discovering properties and enum values, and reading/setting property examples, see references/tom-object-types.md.

7. Validating DAX Expressions

Before saving measure/column expressions, validate them by test-executing against the live model. This catches syntax errors, missing column references, and circular dependencies without persisting bad metadata.

# Validate a DAX expression before adding it as a measure
$testExpr = "SUM('Sales'[Amount]) / COUNTROWS('Sales')"
$cmd = $conn.CreateCommand()
$cmd.CommandText = "EVALUATE ROW(`"@Test`", $testExpr)"
try {
    $reader = $cmd.ExecuteReader()
    $reader.Close()
    Write-Output "VALID"
} catch {
    Write-Output "INVALID: $($_.Exception.Message)"
}

For calculated table expressions, wrap in COUNTROWS:

$tableExpr = "CALENDAR(DATE(2020,1,1), DATE(2030,12,31))"
$cmd.CommandText = "EVALUATE ROW(`"@Count`", COUNTROWS($tableExpr))"

For filter expressions (RLS), test with CALCULATETABLE:

$filterExpr = "'Sales'[Region] = `"West`""
$cmd.CommandText = "EVALUATE CALCULATETABLE(ROW(`"@OK`", 1), $filterExpr)"

8. Transactions and Rollback

SaveChanges() applies all pending modifications in a single implicit transaction. If any object fails validation, the entire batch rolls back automatically.

For multi-step workflows where inspection or rollback is needed before committing:

try {
    # Make changes (not yet persisted)
    $model.Tables["Sales"].Measures["Revenue"].Name = "Total Revenue"
    $model.Tables["Sales"].Measures["Cost"].Name = "Total Cost"

    # Inspect before committing (changes are local to this connection)
    foreach ($m in $model.Tables["Sales"].Measures) {
        Write-Output "  [$($m.Name)]"
    }

    # Commit all changes atomically
    $model.SaveChanges()
    Write-Output "Committed"
} catch {
    # Discard all uncommitted changes
    $model.UndoLocalChanges()
    Write-Output "Rolled back: $($_.Exception.Message)"
}

UndoLocalChanges() discards all modifications made since the last SaveChanges(). This is the rollback mechanism for PBI Desktop; there is no explicit begin/commit transaction API on the local Analysis Services instance.

9. Model Validation

Validate Before Saving

The TOM API does not expose a public Validate() method. Validation happens implicitly during SaveChanges() (which rolls back the entire batch on failure). For pre-save validation, inspect objects manually:

# Check measures have valid expressions (non-empty)
foreach ($m in ($model.Tables | ForEach-Object { $_.Measures }) ) {
    if ([string]::IsNullOrWhiteSpace($m.Expression)) {
        Write-Output "WARNING: Measure [$($m.Name)] in [$($m.Table.Name)] has no expression"
    }
}

# Check relationships reference valid columns
foreach ($rel in $model.Relationships) {
    $sr = [Microsoft.AnalysisServices.Tabular.SingleColumnRelationship]$rel
    if ($sr.FromColumn -eq $null -or $sr.ToColumn -eq $null) {
        Write-Output "WARNING: Relationship [$($sr.Name)] has null column references"
    }
}

# Check for duplicate measure names across tables
$names = @{}
foreach ($m in ($model.Tables | ForEach-Object { $_.Measures })) {
    if ($names.ContainsKey($m.Name)) {
        Write-Output "WARNING: Duplicate measure name [$($m.Name)] in [$($m.Table.Name)] and [$($names[$m.Name])]"
    }
    $names[$m.Name] = $m.Table.Name
}

10. Finding the File Path and Editing Metadata Files

Find the Open File Path

TOM does not expose the .pbix/.pbip file path directly. The most reliable method across all PBI Desktop install types is reading the FileHistory from User.zip in the PBI Desktop app data folder.

Primary method — FileHistory in User.zip (works for Store and non-Store):

# Read the most recently opened file from PBI Desktop's settings
$userZip = "$env:USERPROFILE\Microsoft\Power BI Desktop Store App\User.zip"
# For non-Store installs: "$env:LOCALAPPDATA\Microsoft\Power BI Desktop\User.zip"

Add-Type -Assembly System.IO.Compression.FileSystem
$z = [System.IO.Compression.ZipFile]::OpenRead($userZip)
$entry = $z.Entries | Where-Object { $_.Name -eq 'Settings.xml' }
$reader = New-Object System.IO.StreamReader($entry.Open())
$content = $reader.ReadToEnd()
$reader.Close()
$z.Dispose()

# Extract FileHistory entries (ordered by lastAccessedDate, most recent first)
$history = ($content -split '(?=<Entry)' | Where-Object { $_ -match 'FileHistory' })[0]
$json = [regex]::Match($history, 'Value="s\[(.*?)\]"').Groups[1].Value -replace '&quot;', '"'
$files = $json | ConvertFrom-Json
$files | Select-Object filePath, lastAccessedDate | Format-Table -AutoSize

The first entry is the most recently opened file. Files on the Mac (via Parallels) appear as \\Mac\Home\... paths.

Limitation: This is an imperfect method — it reads recent file history, not the currently open file. If multiple PBI Desktop instances are open, or the most recently accessed file in history isn't the one currently open, the result may be wrong. Confirm with the user if there is any ambiguity.

Fallback — window title (non-Store PBI Desktop only):

Get-Process PBIDesktop -ErrorAction SilentlyContinue | Select-Object Id, MainWindowTitle

Note: Store PBI Desktop (from Microsoft Store / WindowsApps) does not expose the file path in the window title — use the User.zip method above instead.

Fallback — msmdsrv command line (gives workspace path, not file path):

# Useful for finding the port; does NOT reveal the source file path
(Get-WmiObject Win32_Process -Filter "Name='msmdsrv.exe'").CommandLine

Editing PBIP Metadata Files (Connection, Report, Model)

For .pbip projects, metadata files are human-readable JSON/TMDL on disk and can be read and modified directly.

Common targets:

File	Purpose	Skill
<Name>.Report/definition.pbir	Report-to-model connection (byPath or byConnection)	pbip
<Name>.Report/definition/report.json	Report-level settings, theme, filters	pbir-format
<Name>.SemanticModel/definition/*.tmdl	Model metadata (tables, measures, relationships)	tmdl
<Name>.SemanticModel/definition/expressions.tmdl	M/Power Query shared expressions and parameters	tmdl

For syntax, structure, and editing patterns for these files, load the relevant skill from the pbip plugin:

• pbip -- project structure, file types, .pbir connection, forking
• pbir-format -- report.json, visual.json, themes, filters, PBIR JSON schemas
• tmdl -- TMDL syntax, measures, columns, roles, relationships

No Hot-Reload — Close and Reopen Required

IMPORTANT: Power BI Desktop does not watch for external file changes. If you edit metadata files on disk while the report is open, the changes will be silently ignored or overwritten when PBI Desktop next saves.

To apply external file edits:

1. Close Power BI Desktop completely
2. Make your changes to the files on disk
3. Reopen the .pbix or .pbip file

This is different from TOM modifications via $model.SaveChanges(), which apply immediately to the running instance without requiring a restart.

Microsoft Documentation

Topic	URL
TOM API Reference	learn.microsoft.com/en-us/dotnet/api/microsoft.analysisservices.tabular
TOM Overview	learn.microsoft.com/en-us/analysis-services/tom/introduction-to-the-tabular-object-model-tom-in-analysis-services-amo
ADOMD.NET Reference	learn.microsoft.com/en-us/dotnet/api/microsoft.analysisservices.adomdclient
Client Libraries	learn.microsoft.com/en-us/analysis-services/client-libraries
DMV Reference	learn.microsoft.com/en-us/analysis-services/instances/use-dynamic-management-views-dmvs-to-monitor-analysis-services
DAX Reference	dax.guide
Compatibility Levels	learn.microsoft.com/en-us/analysis-services/tabular-models/compatibility-level-for-tabular-models-in-analysis-services

To retrieve current TOM/ADOMD.NET reference docs, use microsoft_docs_search + microsoft_docs_fetch (MCP) if available, otherwise mslearn search + mslearn fetch (CLI). Search based on the user's request and run multiple searches as needed to ensure sufficient context before proceeding.

11. Debugging DAX with EVALUATEANDLOG

EVALUATEANDLOG(<Value>, [Label], [MaxRows]) wraps any DAX expression, returns it unchanged, and emits intermediate results as JSON via a trace event. Works in PBI Desktop only.

Programmatic capture via the TOM Trace API eliminates the need for external tools (DAX Debug Output, SQL Server Profiler, DAX Studio). Subscribe to the DAXEvaluationLog trace event (enum ID 135), capture events with a synchronized ArrayList via Register-ObjectEvent, and parse the JSON from $Event.SourceEventArgs.TextData.

Critical implementation detail: Register-ObjectEvent -Action runs in a separate PowerShell runspace. $global: variables inside the action block do not share scope. Pass a synchronized collection via -MessageData:

$evalEvents = [System.Collections.ArrayList]::Synchronized((New-Object System.Collections.ArrayList))
$job = Register-ObjectEvent -InputObject $trace -EventName "OnEvent" -MessageData $evalEvents -Action {
    $Event.MessageData.Add($Event.SourceEventArgs) | Out-Null
}

Always clear the VertiPaq cache before debug queries; cached results prevent EVALUATEANDLOG from firing:

$server.Execute('{ "clearCache": { "object": { "database": "' + $db.Name + '" } } }') | Out-Null

Common debugging patterns:

Pattern	Approach
Measure chain decomposition	Wrap each intermediate step: EVALUATEANDLOG([Step1], "Label1")
Filter context inspection	Trace CALCULATE with vs without ALL/REMOVEFILTERS
BLANK vs zero detection	Trace the value before a comparison; BLANK = 0 is TRUE in DAX
Variable context trap	Trace VAR value alongside CALCULATE result; proves VAR is not re-evaluated
Grand total diagnosis	Trace numerator + denominator at row vs total grain
Table expression inspection	Wrap CALCULATETABLE result; trace shows actual rows feeding an aggregate

For full setup, JSON payload structure, event batching behavior, and all debugging patterns, see evaluateandlog-debugging.md.

12. Performance Profiling

Programmatic equivalent of DAX Studio's Server Timings. Subscribe to QueryEnd, VertiPaqSEQueryEnd, and VertiPaqSEQueryCacheMatch trace events to measure Formula Engine (FE) vs Storage Engine (SE) time per query.

Key formula: FE time = Total duration - sum(SE scan durations)

Important: VertiPaqSEQueryCacheMatch does NOT support Duration or CpuTime columns; adding them causes $trace.Update() to throw. Only add TextData + EventClass for cache match events.

Workflow:

1. Create trace with performance events (see reference for column compatibility)
2. Clear cache (TMSL clearCache) for cold timings
3. Execute DAX via ADOMD.NET
4. Parse trace events: QueryEnd for total, VertiPaqSEQueryEnd for per-scan SE durations
5. Compare cold vs warm cache to measure cache benefit

Statistical sampling: Single measurements are noisy. Always take 6-12 samples and compare medians (not means) before and after a change. If ranges overlap significantly, the difference is likely noise. Discard the first cold-cache run as warm-up. See the reference for a Measure-QueryMedian helper.

Visual query profiling: Construct SUMMARIZECOLUMNS queries from PBIR visual.json definitions. Column projections become group-by columns; measure projections become measure references; Aggregation.Function maps to SUM (0), MIN (1), MAX (2), COUNT (3), AVERAGE (4).

For full setup, timing interpretation, sampling patterns, and PBIR-to-DAX translation, see performance-profiling.md.

References

Skill references:

• TOM Object Types CRUD - Full CRUD examples for every object type including UDFs, Direct Lake, KPI note
• Annotations and Extended Properties - Standard PBI annotations, Tabular Editor table groups, auto date/time, field parameters, query groups, custom annotations
• Calendar Column Groups - Gregorian, fiscal, and ISO week-based calendar definitions via TOM; time units, primary/associated columns
• DAX Expression Locations - Where DAX appears in a model: measures, calculated columns/tables, calc items, format strings, detail rows, RLS, UDFs
• DAX Pitfalls - Deprecated/not-recommended functions, non-existent functions agents hallucinate from SQL/Python/M, common syntax mistakes, BLANK vs NULL
• EVALUATEANDLOG Debugging - Programmatic DAX debugging via TOM Trace API; capture intermediate results, cache clearing, six debugging patterns for common DAX issues
• Performance Profiling - DAX Server Timings via Trace API; FE/SE time split, cold/warm cache comparison, PBIR visual-to-DAX translation, trace event column compatibility
• Query Listener - Capture live visual DAX queries via DMV polling; interpret query structure, timings, filter patterns
• Export Model - Export to BIM/TMDL via Tabular Editor CLI, fab CLI, or TOM serializer
• VertiPaq Statistics - Column cardinality, dictionary/data size, memory by table, server timings via DMVs
• Refresh Model - All refresh methods (TMSL, TOM RequestRefresh, ADOMD.NET)
• macOS + Parallels Guide - Connecting from macOS when PBI Desktop runs in a Parallels VM
• DAX Library Packages - Installing reusable DAX UDF packages from daxlib.org; DaxLib.SVG, PowerofBI.IBCS, package structure, annotations

CLI tools in bin/:

• daxlib -- CLI for browsing, downloading, and installing DAX library packages from daxlib.org. Script at daxlib.sh (requires bash + jq). Model operations (add/update/remove) call scripts/daxlib-tom/ via dotnet run (requires .NET 8 SDK). On macOS, model operations route through Parallels automatically. See daxlib.md for full command reference.

Agents:

• query-listener -- Dispatch to capture live visual DAX queries in real time; polls DISCOVER_SESSIONS and reports query text + timings

Example scripts in scripts/:

• connect-and-enumerate.ps1 - Connect to PBI Desktop and list all tables, columns, measures, relationships
• explore-model.ps1 - Hierarchical metadata enumeration (tables, columns, measures, hierarchies, partitions, relationships, roles, perspectives, cultures, expressions, data sources)
• query-dax.ps1 - Execute DAX queries via ADOMD.NET with formatted output
• refresh-table.ps1 - Refresh a table or entire model via TMSL with configurable refresh type
• modify-tom-objects.ps1 - Create table, rename measures, set folders/formats, hide columns, create relationship (with undo)
• create-field-parameter.ps1 - Create a field parameter table from a list of measures with all required metadata
• debug-dax.ps1 - Debug DAX with EVALUATEANDLOG trace capture and performance timings; auto-detects port, enumerates model measures, provides Invoke-DebugQuery helper
• connect-from-mac.sh - macOS wrapper that runs PowerShell scripts in a Parallels VM via prlctl exec

External references:

• TOM API Docs
• ADOMD.NET Docs
• Analysis Services Client Libraries
• DAX Guide - use dax.guide/<function>/ for individual function reference