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Overview

Entities represent distinct objects or concepts in your data model (like customers, orders, or products). They enable automatic relationship discovery and intelligent joins between views. When you define entities consistently across views, the semantic layer automatically understands relationships and can join data seamlessly.

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Entity Types

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Primary Entity

Each view should have exactly one primary entity representing the main subject: 
entities:
  - name: order
    type: primary
    description: "Individual order transaction"
    key: order_id

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Foreign Entity

Foreign entities reference objects primarily defined in other views: 
entities:
  - name: customer
    type: foreign
    description: "Customer who placed the order"
    key: customer_id

  - name: product
    type: foreign
    description: "Product in the order"
    key: product_id

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Entity Properties

PropertyTypeRequiredDescription
namestringYesUnique identifier for the entity
typestringYesEntity type: primary or foreign
descriptionstringYesHuman-readable description
keystringNo*The dimension that serves as the entity key (single key)
keysarray[string]No*The dimensions that serve as the entity keys (composite keys)
*Note: Either key or keys must be provided, but not both.

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Simple Entity Keys

Use the key property for entities with a single identifier: 
# views/orders.view.yml
entities:
  - name: order
    type: primary
    key: order_id

  - name: customer
    type: foreign
    key: customer_id

# views/customers.view.yml
entities:
  - name: customer
    type: primary
    key: customer_id
Now queries can seamlessly join these views:
  • “Show total revenue by customer acquisition channel”
  • “What’s the average order value for customers from email campaigns?”

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Composite Keys

For entities with composite keys, use the keys field: 
# views/order_items.view.yml
entities:
  - name: order_item
    type: primary
    description: "Individual line item within an order"
    keys:
      - order_id
      - line_item_id

# views/order_shipments.view.yml
entities:
  - name: order_item
    type: foreign
    description: "Line item being shipped"
    keys:
      - order_id
      - line_item_id
The semantic layer will automatically join these views on both order_id and line_item_id.

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How Entities Enable Joins

When you define entities consistently across views, Oxy automatically:
  1. Identifies relationships between views based on matching entity names
  2. Generates JOIN clauses using the entity keys
  3. Enables cross-view queries without manual join logic

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Example: Multi-View Query

Given these view definitions: 
# views/orders.view.yml
entities:
  - name: order
    type: primary
    key: order_id
  - name: customer
    type: foreign
    key: customer_id

# views/customers.view.yml
entities:
  - name: customer
    type: primary
    key: customer_id

# views/order_items.view.yml
entities:
  - name: order_item
    type: primary
    key: item_id
  - name: order
    type: foreign
    key: order_id
  - name: product
    type: foreign
    key: product_id

# views/products.view.yml
entities:
  - name: product
    type: primary
    key: product_id
Users can ask questions that span all these views:
  • “What’s the total revenue by product category?” (joins orders, order_items, products)
  • “Show me customer lifetime value by acquisition channel” (joins customers, orders)
  • “Which products have the highest return rates?” (joins products, order_items, orders)

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Best Practices

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Naming

  • Use singular nouns (e.g., customer, order, product)
  • Use consistent names across all views
  • Match the business terminology your organization uses

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Design

  • Each view should have exactly one primary entity
  • Add foreign entities for all relationships to other views
  • Ensure entity keys reference valid dimensions in the view

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Performance

  • Index the columns used as entity keys in your database
  • For composite keys, create composite indexes on those columns
  • Consider the cardinality of joins when designing entities

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Common Patterns

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One-to-Many Relationships

# Customer (one) to Orders (many)
# views/customers.view.yml
entities:
  - name: customer
    type: primary
    key: customer_id

# views/orders.view.yml
entities:
  - name: order
    type: primary
    key: order_id
  - name: customer
    type: foreign
    key: customer_id

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Many-to-Many Relationships

# Products (many) to Orders (many) through OrderItems
# views/products.view.yml
entities:
  - name: product
    type: primary
    key: product_id

# views/order_items.view.yml (junction table)
entities:
  - name: order_item
    type: primary
    key: item_id
  - name: product
    type: foreign
    key: product_id
  - name: order
    type: foreign
    key: order_id

# views/orders.view.yml
entities:
  - name: order
    type: primary
    key: order_id

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Hierarchical Relationships

# Employee hierarchy (self-referential)
# views/employees.view.yml
entities:
  - name: employee
    type: primary
    key: employee_id
  - name: manager
    type: foreign
    key: manager_id

Views

Learn about creating views

Dimensions

Define dimensions for your entities

Overview

Back to semantic layer overview