# Model Change > The end-to-end pipeline for changing a semantic model in a local PBIP — confirm the field exists, author, land it in TMDL, validate offline, then prove it against real data. Invoke on "change the model", "add a measure", "add a column", "fix the model", "the number is wrong", "this measure is wrong", "add a relationship", "set up RLS", "add a calculation group", "add a date table", "rename a field", "the model won't open", or any request that ends with a .tmdl file changing. Sequences connect-pbid, power-query, date-table, semantic-model, dax-standard, tmdl, dax-optimisation and refresh-semantic-model, and carries the Desktop-breaking gotchas that a single-skill route misses. - Skill: `insightfulanalytics/model-change` (Agent Skill) - Install (CLI): `npx skillmds@latest add insightfulanalytics/model-change` - Raw SKILL.md: https://api.skillmd.com/api/skills/insightfulanalytics/model-change/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: DevOps & Infra - Author: InsightfulAnalytics (https://skillmd.com/u/insightfulanalytics) - Updated: 2026-09-22 - Page: https://skillmd.com/skills/insightfulanalytics/model-change --- # Model change pipeline Every model change follows the same five steps. Skipping step 1 is how you author a measure against a column that doesn't exist; skipping step 4 is how Desktop refuses to open the project afterwards. **"Change the model" means the local PBIP via direct TMDL edits** — not the live Fabric model — unless the user says otherwise. Confirm which model before touching anything if there is any doubt. ## 0. Before anything - `pbir desktop list` — is Desktop holding this project open? If it is, **coordinate with the user first.** Desktop keeps its own in-memory copy and re-serialises on save, so it will clobber disk edits. - Tim nudges layout inside Desktop between turns. Re-read from disk at task start; never reuse positions or definitions remembered from earlier in the conversation. ## 1. Confirm the shape — don't author blind Load `pbi-desktop:connect-pbid` and query the live instance. The point is to prove the table, column or measure you are about to reference actually exists and holds what you think. - `pbir model -q` fails on this machine (the local-API preview is off). Go straight to the direct ADOMD path in that skill — DAX Studio's `Microsoft.AnalysisServices.AdomdClient.dll` is the one that loads under PowerShell 5.1. Tabular Editor 3's is .NET 8 and throws. - If Desktop isn't open, read the TMDL under `.SemanticModel/definition/tables/`. ## 2. Author Pick the skill that matches the change: | Change | Skill | |---|---| | Measure / calculation | `dax-standard` | | Partition M, folding, a new source | `semantic-models:power-query` | | Relationships, RLS, calc groups, star-schema fixes, model quality | `semantic-models:semantic-model` | | A date/calendar table | `semantic-models:date-table` — don't hand-copy from `Date Table Template` | | Renaming across the project | `pbip:pbip` (the rename cascades into PBIR) | DAX house style: expression starts on **line 2** after the `=`; short lines; the explanatory comment goes **after** the measure name, not above it; prefer `DATEADD` over `SAMEPERIODLASTYEAR`. Never leave a measure in an error state. ## 3. Land it in TMDL Load `pbip:tmdl`. Prefer the Edit tool over script-patching — checkpoint/rewind only restores files changed via Write/Edit, so a python-patched `.tmdl` cannot be rolled back. Three ways to break Desktop's file-open, all of which pass a casual read: - **A calculation group requires `discourageImplicitMeasures`** on the model in `model.tmdl`. Without it Desktop refuses to load the whole project. Check this **every** time a calc group is added, then grep the report pages for bare column projections that relied on implicit aggregation. - **Never leave a blank line after a `///` description.** A dangling description is `Unexpected line type: Empty!` and breaks both Desktop and the modeling MCP. `///` lines sit directly above the object they describe — never as standalone section banners. - Blank lines *between sibling objects* are fine and expected. The failures come only from the two bad spots: after a `///`, or breaking a multi-line expression's indentation. Prefer `///` doc comments over explicit `description` properties — `///` is what Desktop serialises, so round-trip diffs stay stable. ## 4. Validate offline, before Desktop Cheapest first, and it catches syntax errors in seconds rather than after a slow file-open: - `TmdlSerializer::DeserializeDatabaseFromFolder()` via DAX Studio's `Microsoft.AnalysisServices.Tabular.dll` parses the folder and lists tables, columns and measures. TE3's DLL is .NET 8 and will not load under PS 5.1. - An offline `ConnectFolder` connection validates parse and bind only — **it cannot run DAX.** Offline-clean is not query-correct. ## 5. Prove it against real data Desktop holds its own in-memory copy, so a TMDL edit on disk is invisible to a query until it is applied. On Desktop 26.08+ that is the **Apply external changes** banner, which reloads the project in place and keeps the loaded data; close-and-reopen is only needed on older builds, when the edit changes a data source or adds a table that needs a real refresh, or when Desktop has already resolved a field as deleted (that binding stays broken until a full reload). The canonical account, including the UIAutomation snippet that clicks the banner, is the `pbi-desktop:connect-pbid` skill's `references/desktop-lifecycle.md`. Either way, don't reload just to test: > Redefine the measure in the query with `DEFINE MEASURE ''[X new] = …` and select the > old and new side by side in one `ROW()`. That proves the fix against real data with zero > risk to the model. Testing an `ALLSELECTED` measure? Don't sample rows with `FILTER(VALUES(...))` — the filter propagates into `ALLSELECTED` and changes the answer. Build the full axis with `ADDCOLUMNS(VALUES(...), ...)` first, then `FILTER` the result. PowerShell quoting: bracketed names and `{}` break PS string parsing. Pass DAX via single-quoted here-strings (`@'...'@`). ## Wrap-up - Slow measure? *Now* load `semantic-models:dax-optimisation` — it is for tuning, not authoring. - Model-wide audit? `tabular-editor:te-cli` / `bpa-rules`. - Needs a refresh? `semantic-models:refresh-semantic-model`. For a hand-authored PBIP whose first open shows "incomplete or no data", refresh through TOM (`$db.Model.RequestRefresh('Full')` + `SaveChanges()`) — the local-API preview is off, so `pbir desktop refresh` is unavailable. - Report visuals affected by the change? Hand over to `reports:pbir-cli`, and verify with `reports:pbi-verify-loop`. - After fixing a nontrivial error, record the root cause in the project's note under `Vault\Projects\\` and add its row to `Vault\Projects\index.md`.