Context Variable

Context variable system for runtime data management in views.

This module provides the ContextVariable class, which represents typed variables that exist within the runtime context of a view. Context variables enable dynamic data flow, parameter passing, and state management across UI components.

Main Components

Data Types:

CVType enum defines supported data types:

  • INTEGER: Whole numbers

  • DECIMAL: Floating-point numbers

  • STRING: Text values

  • BOOLEAN: True/False logical values

Core Class:

  • ContextVariable: Typed variable with optional default values

Default Values

Context variables support two types of default values:

Literal Defaults:

Fixed values assigned at initialization (e.g., 0, “default”, True)

  • Use for static initial values

  • Set once when variable is created

  • default_value_is_calculated = False

Calculated Defaults:

Dynamic values computed from Parameters or Calculations

  • Use for values derived from other data sources

  • Recomputed when dependencies change

  • default_value_is_calculated = True

Array Variables

Context variables can represent either:

  • Scalar values (is_array=False): Single value of the specified type

  • Array values (is_array=True): List of values of the specified type

Variable Identification

Each ContextVariable has a unique ID used to:

  • Reference the variable in UI bindings

  • Access the variable in event handlers

  • Pass the variable between components

  • Store and retrieve values in runtime context

Use Cases

User Selection Tracking:

Track which item a user has selected for detail viewing or editing

Filter State:

Store current filter criteria for dynamic data filtering

Modal Dialog State:

Pass data to/from modal dialogs (e.g., edit form data)

Computed UI State:

Store calculated values used for conditional rendering

Multi-Step Workflows:

Maintain state across multiple views in a wizard or workflow

Dynamic Validation:

Store validation state or error messages

Examples

Creating a simple context variable:

from daitum_ui import UiBuilder
from daitum_ui.context_variable import CVType

# Create builder
builder = UiBuilder()

# Selected row ID (integer)
selected_row = builder.add_context_variable(
    id="selected_row_id",
    type=CVType.INTEGER,
    default_value=0
)

Creating a context variable with calculated default:

from daitum_model import Parameter

# User role parameter
user_role_param = Parameter(...)

# Is admin flag derived from parameter
is_admin = builder.add_context_variable(
    id="is_admin_flag",
    type=CVType.BOOLEAN,
    default_value=user_role_param  # Calculated from parameter
)

Creating array context variables:

# List of selected item IDs
selected_items = builder.add_context_variable(
    id="selected_item_ids",
    type=CVType.INTEGER,
    is_array=True
)

# List of filter tags
active_tags = builder.add_context_variable(
    id="active_filter_tags",
    type=CVType.STRING,
    is_array=True
)

String context variables for state:

# Current view mode
view_mode = builder.add_context_variable(
    id="current_view_mode",
    type=CVType.STRING,
    default_value="grid"  # Default to grid view
)

# Search query
search_query = builder.add_context_variable(
    id="search_text",
    type=CVType.STRING,
    default_value=""  # Empty by default
)

Decimal context variables for numeric calculations:

# Calculated total price
total_price = builder.add_context_variable(
    id="cart_total",
    type=CVType.DECIMAL,
    default_value=0.0
)

# User-entered discount percentage
discount_percentage = builder.add_context_variable(
    id="discount_pct",
    type=CVType.DECIMAL,
    default_value=10.0
)

Boolean context variables for flags:

# Show/hide detail panel
show_details = builder.add_context_variable(
    id="show_detail_panel",
    type=CVType.BOOLEAN,
    default_value=False
)

# Edit mode toggle
is_editing = builder.add_context_variable(
    id="is_edit_mode",
    type=CVType.BOOLEAN,
    default_value=False
)

Using with calculations:

from daitum_model import Calculation

# Calculation that computes if user has premium access
has_premium_calc = Calculation(...)

# Context variable using calculated default
show_premium_features = builder.add_context_variable(
    id="show_premium_ui",
    type=CVType.BOOLEAN,
    default_value=has_premium_calc
)

Workflow state management:

# Current step in multi-step form (0-indexed)
current_step = builder.add_context_variable(
    id="wizard_step",
    type=CVType.INTEGER,
    default_value=0
)

# Completed steps array
completed_steps = builder.add_context_variable(
    id="completed_wizard_steps",
    type=CVType.INTEGER,
    is_array=True
)
class CVType(*values)[source]

Bases: Enum

Enumeration of supported context variable data types.

Members:

INTEGER: Represents integer numeric values. DECIMAL: Represents floating-point numeric values. STRING: Represents textual values. BOOLEAN: Represents True/False logical values.

INTEGER = 'INTEGER'
DECIMAL = 'DECIMAL'
STRING = 'STRING'
BOOLEAN = 'BOOLEAN'
class ContextVariable(id, type, default_value=None, is_array=False)[source]

Bases: Buildable

Represents a variable available within the view.

A ContextVariable defines a typed value that can be supplied, defaulted, or dynamically calculated at runtime.

id

Unique identifier of the context variable.

type

The declared data type of the variable (e.g., INTEGER, DECIMAL, STRING, BOOLEAN).

default_value

The optional default value to apply when no explicit value is provided.

default_value_is_calculated

Indicates whether the default value is dynamically computed rather than a fixed literal.

is_array

Whether this variable represents a list of values rather than a single scalar value.

__init__(id, type, default_value=None, is_array=False)[source]
Parameters:

  • id (str) – Unique identifier for this context variable.

  • type (CVType) – The data type of the variable value.

  • default_value (bool | int | float | str | Parameter | Calculation | None) – Initial value, or a Parameter/Calculation whose ID is used as a calculated default.

  • is_array (bool) – If True, the variable holds a list of values rather than a scalar.

default_value: bool | int | float | str | None