List Attribute

List attributes store an ordered collection of single element type. Values are represented by a list type in the framework, containing elements of the element type.

In this Terraform configuration example, a list of string attribute named example_attribute is set to the ordered values "one" and "two":

resource "examplecloud_thing" "example" {
  example_attribute = ["one", "two"]
}

Schema Definition

Use one of the following attribute types to directly add a list value to a schema or nested attribute type:

The ElementType field must be defined, which represents the single value type of every element of the list.

In this example, a resource schema defines a top level required list of strings attribute named example_attribute:

func (r ThingResource) Schema(ctx context.Context, req resource.SchemaRequest, resp *resource.SchemaResponse) {
    resp.Schema = schema.Schema{
        Attributes: map[string]schema.Attribute{
            "example_attribute": schema.ListAttribute{
                ElementType: types.StringType,
                Required: true,
                // ... potentially other fields ...
            },
            // ... potentially other attributes ...
        },
    }
}

An element type may itself contain further collection types, if necessary.

In this example, a resource schema defines a top level required list of list of strings attribute named example_attribute:

func (r ThingResource) Schema(ctx context.Context, req resource.SchemaRequest, resp *resource.SchemaResponse) {
    resp.Schema = schema.Schema{
        Attributes: map[string]schema.Attribute{
            "example_attribute": schema.ListAttribute{
                ElementType: types.ListType{
                    ElemType: types.StringType,
                },
                Required: true,
                // ... potentially other fields ...
            },
            // ... potentially other attributes ...
        },
    }
}

If the list value should be the element type of a collection attribute type, set the ElementType field according to the list type. Refer to the collection attribute type documentation for additional details.

If the list value should be a value type of an object attribute type, set the AttributeTypes map value according to the list type. Refer to the object attribute type documentation for additional details.

Configurability

At least one of the Computed, Optional, or Required fields must be set to true. This defines how Terraform and the framework should expect data to set, whether the value is from the practitioner configuration or from the provider logic, such as API response value.

The acceptable behaviors of these configurability options are:

• Required only: The value must be practitioner configured to an eventually known value (not null), otherwise the framework will automatically raise an error diagnostic for the missing value.
• Optional only: The value may be practitioner configured to a known value or null.
• Optional and Computed: The value may be practitioner configured or the value may be set in provider logic when the practitioner configuration is null.
• Computed only: The value will be set in provider logic and any practitioner configuration causes the framework to automatically raise an error diagnostic for the unexpected configuration value.

Custom Types

You may want to build your own attribute value and type implementations to allow your provider to combine validation, description, and plan customization behaviors into a reusable bundle. This helps avoid duplication or reimplementation and ensures consistency. These implementations use the CustomType field in the attribute type.

Refer to Custom Types for further details on creating provider-defined types and values.

Deprecation

Set the DeprecationMessage field to a practitioner-focused message for how to handle the deprecation. The framework will automatically raise a warning diagnostic with this message if the practitioner configuration contains a known value for the attribute. Terraform version 1.2.7 and later will raise a warning diagnostic in certain scenarios if the deprecated attribute value is referenced elsewhere in a practitioner configuration. The framework deprecations documentation fully describes the recommended practices for deprecating an attribute or resource.

Some practitioner-focused examples of a deprecation message include:

• Configure other_attribute instead. This attribute will be removed in the next major version of the provider.
• Remove this attribute's configuration as it no longer is used and the attribute will be removed in the next major version of the provider.

Description

The framework provides two description fields, Description and MarkdownDescription, which various tools use to show additional information about an attribute and its intended purpose. This includes, but is not limited to, terraform-plugin-docs for automated provider documentation generation and terraform-ls for Terraform configuration editor integrations.

Plan Modification

The framework provides two plan modification fields for managed resource attributes, Default and PlanModifiers, which define resource and attribute value planning behaviors. The resource default and plan modification documentation covers these features more in-depth.

Common Use Case Plan Modification

The listdefault package defines common use case Default implementations:

• StaticValue(types.List): Define a static list default value for the attribute.

The listplanmodifier package defines common use case PlanModifiers implementations:

• RequiresReplace(): Marks the resource for replacement if the resource is being updated and the plan value does not match the prior state value.
• RequiresReplaceIf(): Similar to RequiresReplace(), but also checks if a given function returns true.
• RequiresReplaceIfConfigured(): Similar to RequiresReplace(), but also checks if the configuration value is not null.
• UseStateForUnknown(): Copies a known prior state value into the planned value. Use this when it is known that an unconfigured value will remain the same after a resource update.

Sensitive

Set the Sensitive field if the attribute value should always be considered sensitive data. In Terraform, this will generally mask the value in practitioner output. This setting cannot be conditionally set and does not impact how data is stored in the state.

Validation

Set the Validators field to define validation. This validation logic is ran in addition to any validation contained within a custom type.

Common Use Case Validators

HashiCorp provides the additional terraform-plugin-framework-validators Go module which contains validation logic for common use cases. The listvalidator package within that module has list attribute validators such as defining conflicting attributes.

Accessing Values

The accessing values documentation covers general methods for reading schema (configuration, plan, and state) data, which is necessary before accessing an attribute value directly. The list type documentation covers methods for interacting with the attribute value itself.

Setting Values

The list type documentation covers methods for creating or setting the appropriate value. The writing data documentation covers general methods for writing schema (plan and state) data, which is necessary afterwards.