SQRL (version 0.7.4)

sqrlUsage: How to Use the Interface Functions

Description

This material does not describe a single function, but (rather) how to use SQRL interfaces (once created). These interface functions do not have their own static help files, since their names are not known at build time.

Opening and Closing

# Open a connection to the data source.
owl()
# Alternative method (explicit form).
owl("open")
# This is fine (the channel survives).
rm(list = ls(all.names = TRUE))
# Check if the connection is open.
owl("isopen")
# Open a connection and confirm status.
owl()$isopen
# Close the connection.
owl("close")
# Close the connection when not in use.
owl(autoclose = TRUE)

Opening connections in the above way isn't usually necessary, since this occurs automatically, as and when required.

When necessary, the isopen command ‘pings’ the data source, to reliably establish whether or not the connection really is open (including after a network outage or remote closure).

With autoclose = TRUE, owl("isopen") should always return FALSE, whereas owl()$isopen will often return TRUE. This is because the latter command attempts to open a connection, with its return value being the connectivity status immediately after that attempt (before autoclose takes effect and closes the connection). This provides a test of data source reachability and responsiveness, regardless of the autoclose setting.

Submitting Queries

# Submit a query.
owl("select 1")
# Submit another query.
owl("select '", sample(letters, 1), "' from dual")
# Submit a multi-statement query.
owl("use necronomicon; select top ",
    sample(6, 1), " shoggoths from pit")
# Filtering against a set of values.
owl("select columnA from database.table ",
    "where columnB in (", c(2, 3, 5), ")")
# Supplying a query as a list of components.
owl(list("select ", c("'red'", "'blue'")))
# Explicit form.
owl(query = "select 1")
# Recall the result of the last successful query.
owl("result")

If necessary, a connection channel will be opened automatically. The connection will remain open afterwards, unless autoclose is TRUE.

When a query is supplied as components, the pieces are pasted together without any intervening whitespace. To facilitate their use with the SQL in operator, any atomic vectors are collapsed to comma-separated values, beforehand. This (default) behaviour can be altered with the aCollapse and lCollapse parameters (as described in sqrlParams).

Using the query keyword overrides the order of precedence (as detailed below).

As SQRL aims to be flexible on input formatting, the above examples can be extrapolated. For instance, the query parameter could have been set to a list of components (instead of a string).

When a query returns no data (as would “use database”), the interface function returns invisibly.

If a query should fail because of an unexpectedly lost connection, an attempt will be made to re-connect and re-submit. Unless user input is required for authentication, this should go unnoticed. If any temp tables had been in existence, however, then they will have been dropped, which may still lead to an error.

Submitting Queries from File

# Submit a query from file.
owl("my/file.sql")
# Equivalent alternative forms.
owl("my/", "file.sql")
owl(c("my/", "file.sql"))
# Explicit alternative forms.
owl(file = "my/file.sql")
owl(file = c("my/", "file.sql"))

Using the file keyword overrides the order of precedence (as detailed below). In its absence, unnamed arguments are treated as a file path when they point to a readable file.

In the above examples, list(...) works just as well as c(...). Either way, the path components are pasted together without any intervening whitespace (the path not being a literal query).

Submitting Parameterised Queries from File

# Submit a parameterised query from file.
owl("my/file.sqrl", day = 1, month = "May")
# Supplying the arguments in a list.
owl("my/file.sqrl", list(day = 1, month = "May"))
# Supplying the arguments in an explicitly named list.
owl("my/file.sqrl", args = list(day = 1, month = "May"))
# Supplying both the query and its arguments in a list.
owl(list(file = "my/file.sqrl", day = 1, month = "May"))
owl(list(file = c("my/", "file.sqrl"),
         args = list(day = 1, month = "May")))

To be clear, the phrase “parameterised query” is not meant in the sense of prepared or parameterised statements (as per package RODBCext). In SQRL, parameter substitution occurs within R (locally), with the resulting string being passed to the ODBC driver as an ordinary query. Refer to sqrlScript for the details.

The use of the args keyword is optional when all list members have syntactically valid names (in the sense of base::make.names). Any such lists are automatically interpreted as collections of named arguments (and are unpacked to those collections). Query arguments called, for instance, file, proc, or query, may need to be wrapped in args to ensure they are treated as intended, and not as query (script) specifiers.

In keeping with SQRL's intended flexibility around input formatting, any of the file path specification methods of the previous section could also be used here.

Stored Procedures

# Import procedures from file.
owl(library = "my/library.sqrl")
# List procedure names.
owl("library")
# List procedure definitions.
owl("Library")
# Run a named procedure.
owl("my procedure")
# Equivalent explicit form.
owl(proc = "my procedure")
# Run a parameterised procedure.
owl("Cropp River Rainfall", date = Sys.Date() - 1)
# Empty the library.
owl(library = NULL)

As detailed below, procedures top the order of precedence. Consequently, the proc keyword is an entirely optional transparency device. In its absence, unnamed arguments are treated as the name of a procedure when they name a procedure within the library.

The library-file procedure-definition format is described in sqrlScript. The path to such a file (i.e., the value of the library keyword) can be supplied in any of the file-path formats of the previous sections (that is, as a list or vector of components).

Any of the file-path and/or query-argument specification formats seen in the previous two sections can equally be used with procedure names. The only difference is to replace any file keyword with the proc keyword.

Querying Metadata

# Get information on source data types.
owl("typeinfo")
# List all tables.
owl("tables")
# List all tables within a database (schema).
owl("tables", "mydatabase")
# Get information on the columns of a particular table.
owl("columns", "my.table")

The typeinfo, tables, and columns commands are simple (reduced functionality) wrappers about RODBC::sqlTypeInfo, RODBC::sqlTables, and RODBC::sqlColumns, respectively. These features are dependent upon the support of your DBMS. For some sources, the believeNRows parameter may need to be FALSE.

Reviewing Settings

# Get the associated source definition.
owl("source")
# Get the value of one named parameter.
owl("uid")
# Alternative method (pings the source).
owl()$uid
# List the values of all parameters.
owl("config")
# List a subset of parameter values.
owl("settings")

The settings subset is intended for restoring RODBC and/or SQRL parameter values at the end of a script that changed some. An example of this is given in sqrlScript. It can also be used to transfer parameter values between sources.

Setting Parameters

# Set a parameter value.
owl(stringsAsFactors = FALSE)
# Set multiple parameter values.
owl(max = 1000, na.strings = c("NA", "-", ""))
# Set multiple values from a list.
owl(list(case = "toupper", scdo = FALSE))
# Set values from a list (explicit form).
owl(config = list(visible = TRUE, autoclose = TRUE))
# Import values from source 'wol'.
owl(config = wol("settings"))
# Import values from a configuration file.
owl(config = "my/config/file.txt"))
# Import one value from a file.
owl(pwd = c("path/", "to/", "file", ".txt"))
# Reset parameters to their default values.
owl(reset = c("errors", "nullstring"))

The driver and dsn parameters accept file paths as their values. For all other parameters, values are extracted from within any specified files.

Assigning visible TRUE authorises modification of the global prompt option. When running R.exe, Rterm.exe or Rgui.exe on a Windows operating system, this also authorises modification of theR window title.

Calling reset on its own, as in owl("reset"), does nothing.

Further alternative input formats appear in the examples section of sqrlParams.

Changing the Interface

# Change the interface.
owl(interface = "O")
# Change it back.
O(interface = "owl")

Changing the interface is just a particular case of setting a parameter.

If the proposed new interface name already belongs to some other function within the R search path, then the change request will be denied (unless that name is remove, in which case the current interface function will be deleted).

A successful change deletes the previous interface.

Listing Data Sources

# See the data sources and their interfaces.
owl("sources")

This is equivalent to calling sqrlSources().

Getting Help

# Get help on 'owl' (alternative forms).
owl("help")
owl("?")
# Obtain help, in specific formats.
owl("help text")
owl("help html")

The above calls will attempt to provide help tailored for the specific interface, and will fall back to these notes (help(sqrlUsage) or ?sqrlUsage) should that fail.

Removing the Source

# Deregister the associated source.
owl("remove")

This closes any open connection to the data source, deletes the interface function (owl), and deregisters the source from SQRL.

Order of Precedence

When unnamed arguments are supplied, such as in owl("something"), SQRL interprets those arguments with the following order of precedence:

1. Procedure names (in the library),

2. File paths (of SQL or SQRL scripts),

3. Special words (“close”, “config”, etc.),

4. Parameter names (optionally followed by values),

5. Literal SQRL script (including pure SQL).

Hence, if a file called (say) use database should exist, then owl("use database") submits the content of that file (rather than the apparent SQL command). Such conflicts can be resolved by assigning the unnamed arguments to the appropriate keyword (file, proc, or query). In this case, the new command would be owl(query = "use database").

Details

Once you have a named interface (created either automatically, on loading of the SQRL namespace, or manually, via sqrlSource), it can be used to communicate with the associated data source. Connection handles and communication parameters are managed under the hood.

The following sections provide usage examples for an interface called owl. The names of your own interface functions can be discovered by calling sqrlSources().

See Also

sqrlAll, sqrlConfig, sqrlParams, sqrlScript

Examples

# NOT RUN {
# Some default values, for demonstration purposes.
x <- 1; y <- 2

# Define a new SQRL source and its interface. The DSN need
# not exist, but this will fail (by design) if a function
# called 'owl' already exists on the R search path.
sqrlSource("owl", dsn = "HundredAcreWood")

# This (ordinarily pointless) SQRL script contains no SQL,
# which allows it to run even when the DSN does not exist
# (there being no need to open a connection). In this case,
# the x and y variables are implicitly inherited.
owl("<R> x * y")

# Explicitly assign x, while inheriting y.
owl("<R> x * y", x = 2)

# Write the script to file.
myfile <- tempfile()
writeLines("<R> x * y", myfile)

# Run the script from file, inheriting variables.
owl(myfile)

# Run the script from file, with explicit arguments.
# (These are all equivalent.)
owl(myfile, x = 2, y = 3)
owl(myfile, list(x = 2, y = 3))
owl(myfile, args = list(x = 2, y = 3))
owl(file = myfile, x = 2, y = 3)
owl(file = myfile, list(x = 2, y = 3))
owl(file = myfile, args = list(x = 2, y = 3))
owl(list(file = myfile, x = 2, y = 3))
owl(list(file = myfile, args = list(x = 2, y = 3)))

# With the file path specified as components.
owl(dirname(myfile), "/", basename(myfile), x = 2, y = 3)
owl(file = c(dirname(myfile), "/", basename(myfile)),
    args = list(x = 2, y = 3))

# Construct a library file (of procedure definitions).
mylibraryfile <- tempfile()
writeLines(c("<proc 'proc-a'> <R> x * y </proc>",
             "<proc 'proc-b'> <R> x + y </proc>"),
           mylibraryfile)

# Import procedures from file (to owl's library).
owl(library = mylibraryfile)

# Run the imported procedures.
owl("proc-a")
owl("proc-b", x = 2, y = c(3, 4))

# Review the last result.
owl("result")

# Clean-up.
unlink(c(myfile, mylibraryfile))
owl("remove")
# }