Add Power BI modeling skill

2026-02-23 11:55:12 +00:00 · 2026-02-03 12:29:33 +03:00
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+# Relationships in Power BI
+
+## Relationship Properties
+
+### Cardinality
+| Type | Use Case | Notes |
+|------|----------|-------|
+| One-to-Many (*:1) | Dimension to Fact | Most common, preferred |
+| Many-to-One (1:*) | Fact to Dimension | Same as above, direction reversed |
+| One-to-One (1:1) | Dimension extensions | Use sparingly |
+| Many-to-Many (*:*) | Bridge tables, complex scenarios | Requires careful design |
+
+### Cross-Filter Direction
+| Setting | Behavior | When to Use |
+|---------|----------|-------------|
+| Single | Filters flow from "one" to "many" | Default, best performance |
+| Both | Filters flow in both directions | Only when necessary |
+
+## Best Practices
+
+### 1. Prefer One-to-Many Relationships
+```
+Customer (1) --> (*) Sales
+Product  (1) --> (*) Sales
+Date     (1) --> (*) Sales
+```
+
+### 2. Use Single-Direction Cross-Filtering
+Bidirectional filtering:
+- Impacts performance negatively
+- Can create ambiguous filter paths
+- May produce unexpected results
+
+**Only use bidirectional when:**
+- Dimension-to-dimension analysis through fact table
+- Specific RLS requirements
+
+**Better alternative:** Use CROSSFILTER in DAX measures:
+```dax
+Countries Sold = 
+CALCULATE(
+    DISTINCTCOUNT(Customer[Country]),
+    CROSSFILTER(Customer[CustomerKey], Sales[CustomerKey], BOTH)
+)
+```
+
+### 3. One Active Path Between Tables
+- Only one active relationship between any two tables
+- Use USERELATIONSHIP for role-playing dimensions:
+
+```dax
+Sales by Ship Date = 
+CALCULATE(
+    [Total Sales],
+    USERELATIONSHIP(Sales[ShipDate], Date[Date])
+)
+```
+
+### 4. Avoid Ambiguous Paths
+Circular references cause errors. Solutions:
+- Deactivate one relationship
+- Restructure model
+- Use USERELATIONSHIP in measures
+
+## Relationship Patterns
+
+### Standard Star Schema
+```
+     [Date]
+       |
+[Product]--[Sales]--[Customer]
+       |
+   [Store]
+```
+
+### Role-Playing Dimension
+```
+[Date] --(active)-- [Sales.OrderDate]
+   |
+   +--(inactive)-- [Sales.ShipDate]
+```
+
+### Bridge Table (Many-to-Many)
+```
+[Customer]--(*)--[CustomerAccount]--(*)--[Account]
+```
+
+### Factless Fact Table
+```
+[Product]--[ProductPromotion]--[Promotion]
+```
+Used to capture relationships without measures.
+
+## Creating Relationships via MCP
+
+### List Current Relationships
+```
+relationship_operations(operation: "List")
+```
+
+### Create New Relationship
+```
+relationship_operations(
+  operation: "Create",
+  definitions: [{
+    fromTable: "Sales",
+    fromColumn: "ProductKey",
+    toTable: "Product", 
+    toColumn: "ProductKey",
+    crossFilteringBehavior: "OneDirection",
+    isActive: true
+  }]
+)
+```
+
+### Deactivate Relationship
+```
+relationship_operations(
+  operation: "Deactivate",
+  references: [{ name: "relationship-guid-here" }]
+)
+```
+
+## Troubleshooting
+
+### "Ambiguous Path" Error
+Multiple active paths exist between tables.
+- Check for: Multiple fact tables sharing dimensions
+- Solution: Deactivate redundant relationships
+
+### Bidirectional Not Allowed
+Circular reference would be created.
+- Solution: Restructure or use DAX CROSSFILTER
+
+### Relationship Not Detected
+Columns may have different data types.
+- Ensure both columns have identical types
+- Check for trailing spaces in text keys
+
+## Validation Checklist
+
+- [ ] All relationships are one-to-many where possible
+- [ ] Cross-filter is single direction by default
+- [ ] Only one active path between any two tables
+- [ ] Role-playing dimensions use inactive relationships
+- [ ] No circular reference paths
+- [ ] Key columns have matching data types