Blocks with Computed Fields

Some providers, resources, and data sources include repeatable nested blocks in their attributes. Some blocks contain fields with Computed: true, which means that the provider code can define the value or that it could come from the output of terraform apply (e.g., the ID of an EC2 instance).

This page explains how to migrate computed-only blocks from SDKv2 to the Framework. Refer to Blocks if you are looking for information about migrating blocks that are practitioner configurable.

SDKv2

In SDKv2, blocks are defined by an attribute whose type is either TypeList or TypeSet, and whose Elem field is set to a schema.Resource that contains a map of the block's attribute names to corresponding schemaSchema structs.

map[string]*schema.Schema{
    "example": {
        Type:     schema.TypeList,
        Computed: true,
        Elem: &schema.Resource{
            Schema: map[string]*schema.Schema{
                "nested_example": {
                        Type:        schema.TypeString,
                        Computed:    true,
                        /* ... */

Framework

In the Framework, when working with protocol version 5, computed blocks are implemented using a ListAttribute which has an ElementType of types.ObjectType.

map[string]schema.Attribute{
"example": schema.ListAttribute{
    Computed: true,
    ElementType: types.ObjectType{
        AttrTypes: map[string]attr.Type{
            "nested_example":  types.StringType,
            /* ... */

In the Framework, when working with protocol version 6, we recommend that you define computed blocks using nested attributes. This example shows usage of ListNestedAttribute as this provides configuration references with list index syntax as is the case when using schema.TypeList in SDKv2. SingleNestedAttribute is a good choice for single underlying objects which results in a breaking change but also allows dropping [0] in configuration references.

map[string]schema.Attribute{
"example": schema.ListNestedAttribute{
    Computed: true,
    NestedObject: schema.NestedAttributeObject{
        Attributes: map[string]schema.Attribute{
            "nested_example": schema.StringAttribute{
                Computed: true,
                /* ... */

Migration Notes

• When using protocol version 5 specify ElementType as types.ObjectType when migrating blocks that are computed from SDKv2 to Framework.
• When using protocol version 6, use nested attributes when migrating blocks that are computed from SDKv2 to Framework.

Example

SDKv2

The following example shows the implementation of the example_nested_block with SDKv2.

Schema: map[string]*schema.Schema{
"example_nested_block": {
        Type:     schema.TypeList,
        Computed: true,
        Elem: &schema.Resource{
            Schema: map[string]*schema.Schema{
                "example_block_attribute": {
                    Type:        schema.TypeString,
                    Computed:    true,
                    /* ... */
                },

Framework

The following shows the same section of provider code after the migration.

This code defines the example_nested_block block as an attribute on the schema, where the types.ObjectType is being used to define the nested block.

map[string]schema.Attribute{
    "example_nested_block": schema.ListAttribute{
        ElementType: types.ObjectType{
            AttrTypes: map[string]attr.Type{
                "example_block_attribute":  types.StringType,
            },
        },
        Computed:            true,
        /* ... */