A one-off table contains information about the templates that an address book provider supports for creating new recipients. One-off tables are implemented by address book providers, individual address book containers, and by MAPI, and can be persistent or temporary.
Note Do not confuse the templates in one-off tables with template identifiers; while their purposes are similar, their code constructs are nothing alike. Templates are used to create recipients of a particular type while template identifiers are used to bind the data of one recipient belonging to a host provider with code to support another recipient belonging to a foreign provider.
Clients create new recipients:
In both scenarios, an address book provider is asked to return a one-off table. Address book providers can implement either a single one-off table to be used in both situations or a unique one-off table for each situation.
When the recipient will be included with an outgoing message, MAPI calls the address book provider's IABLogon::GetOneOffTable method to retrieve its one-off table. The one-off table includes templates which allow a user to enter information resulting in the creation of a recipient with a valid address. MAPI registers for notifications on this table, keeping it open so that changes can be reflected to the user. MAPI releases the table only when its subsystem or address book status objects' IMAPIStatus::ValidateState method is called.
When the recipient will be added to a container, MAPI makes a different call, invoking the container's IMAPIProp::OpenProperty method to retrieve its PR_CREATE_TEMPLATES property. The set of templates included in this one-off table represents the types of recipients that can be added to the container. For example, mail servers often expose one container for every gateway that is installed so that each container only holds addresses specific to the corresponding gateway.
MAPI provides a one-off table that includes its own templates as well as templates from each of the address book providers in the session. MAPI provides a generic template that can be used to create a new recipient for any address type, assuming that the user knows its format. Address book providers use this one-off table by calling IMAPISupport::GetOneOffTable. Each of the templates included in the MAPI one-off table results in the creation of recipients with valid recipient addresses.
Address book providers typically supply one template for every address type they support. However, support for templates is not required. Address book providers that do not allow the creation of new addresses can return MAPI_E_NO_SUPPORT when MAPI calls to request a one-off table. Address book providers that do allow new address creation but do not supply any templates can call IMAPISupport::GetOneOffTable to use the templates listed in the MAPI one-off table.
The following properties make up the required column set in one-off tables:
| PR_ADDRTYPE | PR_DEPTH |
| PR_DISPLAY_NAME | PR_DISPLAY_TYPE |
| PR_ENTRYID | PR_INSTANCE_KEY |
| PR_SELECTABLE |
PR_ADDRTYPE indicates the type of address that can be associated with the new recipient created with the template.
PR_DISPLAY_NAME and PR_DISPLAY_TYPE associate data with the new recipient. PR_DISPLAY_NAME contains a character string that identifies the new recipient and PR_DISPLAY_TYPE contains a constant that identifies the type of icon to be displayed with the row. Templates for messaging users have their PR_DISPLAY_TYPE column set to DT_MAILUSER; templates for distribution lists have their PR_DISPLAY_TYPE column set to DT_DISTLIST.
PR_ENTRYID is the entry identifier of the template to be used to create a new recipient. This entry identifier can be passed to future IAddrBook::NewEntry, IAddrBook::OpenEntry, and IABContainer::CreateEntry calls. Containers set the PR_ENTRYID column of their row for the default messaging user template to PR_DEF_CREATE_MAILUSER and the PR_ENTRYID column of their row for the default distribution list template to PR_DEF_CREATE_DL.
PR_DEPTH is used to support the hierarchical display of the entries in a one-off table by indicating the level of indentation for the template. Although one-off tables can be displayed either as a flat list or a hierarchical display, the latter is preferable and address book providers should support it by setting the PR_DEPTH column for each row appropriately. PR_DEPTH is zero-based; rows with a value of 0 in their PR_DEPTH column are not indented. The higher the value of PR_DEPTH, the more the row is indented. For example, rows with PR_DEPTH set to 1 are indented one tab while rows with PR_DEPTH set to 3 are indented three tabs.
PR_SELECTABLE is used to indicate whether or not a row in the table represents a template that can be selected and used to create a new recipient. Although most rows in a one-off table do represent templates, providers can include non-template rows. For example, a provider might want to organize the one-off table by template type, including a category row that appears in the display but is not used for recipient creation.
The following dialog box illustrates a one-off table with five rows, four of which represent templates and have their PR_SELECTABLE column set to TRUE. The one non-template row, indicated by the text "Special Address Types," has its PR_SELECTABLE column set to FALSE.