Domino Code Fragment

Code Name* @DbColumn(ODBC)	Date* 04/28/2024	Source (or email address if you prefer)* Rlatulippe@romac.com IP address:.3.142.53.68
Description*	Type* Formula	Categories* (Misc)

Implementation:	Required Client:	Server:
Limitations:	Comments: @DbColumn can only retrieve data; it can't add, delete, or modify data @DbColumn is intended mainly for keyword formulas. Instead of hardcoding a list of keywords and then periodically updating that list, @DbColumn lets you dynamically retrieve a list of values from an external database table.

Files/Graphics attachments (if applicable): Code:
@DbColumn(ODBC : NoCache; data_source ; user_ID1 : user_ID2; "password1" : "password2"; table ; column : null_handling; Distinct : sort )

Parameters
"ODBC"

Keyword. Indicates that you are accessing an ODBC data source.

"NoCache"

Keyword. Optional. If you want to ensure that Notes retrieves the latest information for every lookup, specify this option, as in ODBC:NoCache. Omit NoCache if you want the results of the lookup to be

cached

, that is, stored for re-use. Each subsequent lookup to the same location (within the same Notes session and so long as the database executing this lookup remains open) will simply reuse that information.

If you omit NoCache, you do not have to replace it with anythingthe lookup results are cached automatically, but you may specify "Cache" for readability.

"data_source"

Text. The name of the external data source being accessed. A data source indicates the location of one or more database tables.

"user_ID1" : "user_ID2"

Text list. The user IDs needed to connect to the external database. You may need up to two IDs, depending on the DBMS being accessed.

"password1" : "password2"

Text list. The passwords required by the user IDs.

"table"

Text. The name of the database table being accessed.

"column"

Text. The name of the column from which data is being retrieved.

"null_handling"

Text. Specifies how null values are treated when the data is retrieved.

"Distinct"

Keyword. Optional. Removes duplicate values from the list before returning data to Notes.

"sort"

Keyword. Specify "Ascending" to sort the list of values into ascending order before it is returned to Notes; specify "Descending" to sort the list in descending order.

Return value
valuesFound

Text, number, date-time, or a list of these types. The values found in the

column

you indicated.

Specifying NoCache
The decision to use NoCache is based on performance. Forcing Notes to connect to the database and retrieve the same information again and again takes time, and slows overall performance. However, if you expect data to be changing on a frequent basis, it's worth the extra time to get uptodate information.

For example, if youre using lookups to a database that stores customer addresses, its generally safe to use caching because you dont expect the addresses to change very often. But if youre using a lookup to a database where stock prices are stored, and that database gets updated hourly, its safer to omit caching and force a new lookup each time.

Note

If you use the option button or the check-box user interface for a keywords field, Notes updates the keyword list only when the document is composed or is loaded for editing. If you use the Standard user interface for the list, the keyword list is additionally updated every time the document is recalculated.

Specifying the data source
The data source name can contain up to 32 alphanumeric characters.

@DbLookup can access data sources that have already been registered in the ODBC.INI file (or similar registry on platforms on other than Windows). It can also autoregister a data source not present in the registry. For autoregistration, specify the data source as "data_source" : "type" : "path" where data_source is the name to be assigned, type identifies the DBMS (for example, "Oracle7"), and path is a server name, directory, or other string that locates the DBMS.

Specifying IDs and passwords
You only need these arguments if your DBMS requires them.

Instead of storing the IDs in the @DbColumn formula, you can replace them with null strings (""). If an ID is required, the user will be prompted for it. This is useful when you do not want other designers to see tDs, or when you want users to enter their own IDs when accessing external data. However, you must include IDs and passwords in formulas that run automatically (such as an agent) because these formulas don't prompt for information.

The user IDs and passwords for accessing a data source are required only once per Notes database session, as long as that database remains open. If the user opens another Notes database and executes a formula that accesses the same data source, the user ID and password will be required again.

Password parameters are necessary only when ID parameters are specified. Like the IDs, the passwords can either be stored in the @DbColumn formula, or prompted for by substituting the null string. If the database password is null, you can omit it from the formula.

For example, for the full ID/password specification, enter:

"";"" (two null strings, separated by a semi-colon) to specify no ID and password, or to prompt for both
"user_ID1":"password1" to specify one user ID and password combination
"user_ID1":"user_ID2";"password1":"password2" to specify two user ID and password combinations

Specifying the table name
You can optionally include the name of the table's owner to remove ambiguity; use the format "owner_name. table_name", with a period to separate the owner name from the table name. For example:

"dbo.author"

Table can also refer to a database view in the DBMS being accessed.

Specifying null handling
Normally, null values are ignored and the resulting list is shortened (same as using the Discard option described below).

To control how null values are handled, specify one of the following, appended to the column parameter with a colon:

Generates "Fail" this error message if the column of data contains any null values:

Null values found - canceling @Db function

No data is returned with the message.

Discards "Discard" the null values, thus shortening the returned list of values. If one or more values are discarded when the @DbColumn formula is executed, Notes displays this message on the status bar:

Caution: NULL values discarded from @Db list.

Value "Replacement value" that you specify to be used instead of null values. The replacement value must be a quoted string, but if the column is numeric or date-time, the string must be convertible to that type.
If your formula includes a sort keyword, the list of values to be returned is sorted before the replacement values are inserted. During sorting, all null values are placed at the beginning of the list for an ascending sort; and at the end for a descending sort. They are not replaced until sorting is complete. This can result in a list that has some values sorted incorrectly. For example, if you specify "zz" as your replacement value, all the "zzz" values will appear at the beginning of the list, even if you sorted it in ascending order.
If one or more values are replaced when the @DbColumn formula is executed, Notes displays this message on the status bar:

Caution: NULL value replaced with user-defined value in @Db list

Generally, the replacement value should be one that is not likely to appear in the list as valid data; for example, if the column is text, your replacement value might be "***" so you can easily find those values in Notes.

Specifying Distinct
The Distinct keyword is similar to @Unique in Notes, except that Distinct ensures that duplicate values are removed before the data is returned to Notes. Using Distinct instead of @Unique has two advantages:

The formula operates more quickly because the additional work is performed outside of Notes.
You can potentially retrieve a larger amount of useful data into Notes--since the duplicate values are removed at the back-end, more unique values can be returned to Notes.

Note Distinct is not supported by all ODBC drivers. If there are null values in the data and you specify Distinct, one null is usually returned.

Specifying sort
If you use the Distinct keyword, you can append the sort parameter to it with a colon. Use one these keywords for the sort parameter to specify sorting of the return values:

Ascending sorts the list in ascending order.
Descending sorts the list in descending order.

If no sort keyword is specified, values are returned in arbitrary order.

Note The sort keywords are not supported by all ODBC drivers. If you attempt to use both Ascending and Descending in your formula, Notes displays an "Invalid argument" message.

If multiple values are returned, they are formatted as a list and are separated with the multi-value separator designated for the current field.

@DbColumn can return no more than 55K bytes of data. Use the following equations to determine how much of your data can be returned with @DbColumn.

For lookups that return text:
2 + (2 * number of entries returned) + total text size of all entries
Each text string is limited to 511 bytes; if only one text string is returned, it is limited to 55K bytes.
For lookups that return numbers or dates:
(10 * number of entries returned) + 6

If the user's NOTES.INI file includes the statement

NoExternalApps=1

the @DbColumn formula is disabled. The user will not see an error message; the formula fails to execute. This applies to @DbColumn only when you use it with ODBC.