Expanding omopgenerics

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Introduction

omopgenerics defines an ecosystem of methods and classes particularly the class that can be expanded. Currently there are two packages that define cdm sources:

omopgenerics defines the source that defines the implementation of a ‘local’ (in memory) cdm source.
CDMConnector defines the source that defines a general implementation for DBI connections.

In this vignette we explain how to expand the omopgenerics ecosystem defining more sources.

The source object

First we need to define a function to create our source object: the source object must be an object (usually a list) that contains several attributes that will be used in the methods to fulfill their purpose. Finally we have to assign a class to our source and validate it with omopgenerics::newCdmSource(). The function has an argument to assign a sourceType that must be a character vector that identifies the name of the source. This is what will be retrieved by the omopgenerics::sourceType() function and it will be useful to identify how the source of the cdm_reference has been created.

Example how the creation of a new source would look like:

myCustomSource <- function(argument1, argument2, ...) {
  # pre calculation and validation of arguments
  ...
  
  # create the source object
  obj <- list(x = x, y = y, ...) # this way you would access the attributes like: obj$x
  # or
  obj <- structure(.Data = list(), x = x, y = y, ...) # this you would access the attributes like: attr(obj, "x")
    
  # assign class
  class(obj) <- "my_custom_source"
  
  # validation
  omopgenerics::newCdmSource(src = obj, sourceType = "my_custom_type")
}

If the first function that we create is myCustomSource() the validation with omopgenerics::newCdmSource() will fail as inside the methods are checked to be defined and work properly.

Methods

You will need to write 4 to 7 methods for your new <my_custom_source>:

insertTable required To insert local data into your source.
compute required To compute a ‘query’ into a table in your source.
listSourceTables required To list the data present into your source.
dropSourceTable required To drop a table from your source.
readSourceTable recommended To read a table from your source.
insertCdmTo recommended To insert a cdm into your source.
summary recommended To summarise and report the properties of your source.

`insertTable`

Purpose: To insert a local table into your source object.

Arguments:

cdm The cdm argument will be your source object created with myCustomSource() function.
name The name to identify that table in your source.
table A local <tibble> to insert in your source.
overwrite (by default TRUE), whether to overwrite if the table exists in the database.
temporary (by default FALSE), whether the table must be temporary.

Output: The output of a insertTable must be a cdm_table so your function must at the end validate it with omopgenerics::newCdmTable().

Sketch of how the function should look like:

#' @export
#' @importFrom omopgenerics insertTable
insertTable.my_custom_source <- function(cdm, name, table, overwrite, temporary) {
  # code to insert the table into your source
  x <- "...." # it must be a reference to your table
  
  # validate output
  omopgenerics::newCdmTable(table = x, src = cdm, name = name)
}

`listSourceTables`

Purpose: To list tables that are present in the source.

Arguments:

cdm The cdm argument will be your source object created with myCustomSource() function.

Output: A character vector with the names of tables present in source, empty identifiers "" will be eliminated by omopgenerics.

Sketch of how the function should look like:

#' @export
#' @importFrom omopgenerics listSourceTables
listSourceTables.my_custom_source <- function(cdm) {
  # code to list the tables present in source (cdm)
  x <- "...."
  
  return(x)
}

`readSourceTable`

Purpose: To read tables that are present in the source.

Arguments:

cdm The cdm argument will be your source object created with myCustomSource() function.
name Name to identify the table in your source.

Output: The output of a readSourceTable must be a cdm_table so your function must at the end validate it with omopgenerics::newCdmTable().

Sketch of how the function should look like:

#' @export
#' @importFrom omopgenerics readSourceTable
readSourceTable.my_custom_source <- function(cdm, name) {
  # code to read the table 'name' from source.
  x <- "...."
  
  # validate as cdm_table
  omopgenerics::newCdmTable(table = x, src = cdm, name = name)
}

`dropSourceTable`

Purpose: To drop a table from your source.

Arguments:

cdm The cdm argument will be your source object created with myCustomSource() function.
name Name identifier for the table that you want to drop.

Output: The output is ignored, would recommend to return the source.

Sketch of how the function should look like:

#' @export
#' @importFrom omopgenerics dropSourceTable
dropSourceTable.my_custom_source <- function(cdm, name) {
  # code to drop the table `name` present in source (cdm)
  
  return(invisible(cdm))
}

`insertCdmTo`

Purpose: To insert a cdm to your source.

Arguments:

cdm A cdm reference from a different source. Recommend to collect each table before inserting.
to The ‘to’ argument will be your source object created with myCustomSource() function.

Output: The output should be the cdm reference object inserted in your to source.

Sketch of how the function should look like:

#' @export
#' @importFrom omopgenerics dropSourceTable
insertCdmTo.my_custom_source <- function(cdm, to) {
  # example of how it can look like:
  tables <- names(cdm) |>
    rlang::set_names() |>
    purrr::map(\(x) omopgenerics::insertTable(cdm = to, name = x, table = dplyr::as_tibble(cdm[[x]])))
  
  omopgenerics::newCdmReference(
    tables = tables, 
    cdmName = omopgenerics::cdmName(x = cdm), 
    cdmVersion = omopgenerics::cdmVersion(x = cdm)
  )
}

The content of the function can vary depending of your source.

`summary`

Purpose: To summarise the metadata of your source object.

Arguments:

object The ‘object’ argument will be your source object created with myCustomSource() function.
... For consistency.

Output: A named list of metadata of the source, each element must be a string of length 1.

Sketch of how the function should look like:

#' @export
summary.my_custom_source <- function(object, ...) {
  # extract metadata
  metadata1 <- "..."
  metadata2 <- "..."
  metadata3 <- "..."
  
  list(metadata1 = metadata1, metadata2 = metadata2, metadata3 = metadata3)
}

`compute`

This function works slightly different to the rest the input it will be a query instead of the source object.

Purpose: To compute a table into a permanent placeholder in your source.

Arguments:

x Query to compute.
name The name to identify the resultant table in your source.
temporary (by default FALSE), whether the table must be temporary.
overwrite (by default TRUE), whether to overwrite if the table exists in the database.
... For consistency.

Output: The output of a compute must be a reference to your table in your source data, it will be converted later to a cdm_table (but you do not have to worry about that).

Sketch of how the function should look like:

#' @export
#' @importFrom dplyr compute
compute.my_custom_source <- function(x, name, overwrite, temporary, ...) {
  # code to compute the table into your source
  x <- "...." # it must be a reference to your table
  return(x)
}

The cdm reference object

Finally every <cdm_source> class object would also need a function to create a to do that you just have to read all the tables that you want to include in your cdm object. tables must be a list of with the same source.

cdmFromMyCustomSource <- function(argument1, argument2, ...) {
  # read and prepare the cdm tables
  ...
  
  # return the cdm object
  omopgenerics::newCdmReference(
    tables = tables, # list of cdm and achilles standard tables
    cdmName = "...", # usually provided as input, but also you might want to search in the cdm_source
    cdmVersion = "..." # either "5.3" or "5.4"
  )
}

If you want to add to your object do it after the initial cdm creation like:

# read from source 
cdm <- readSourceTable(cdm = cdm, name = "my_cohort")

# or insert from local
cdm <- insertTable(cdm = cdm, name = "my_cohort", table = localCohort)
cdm$my_cohort <- cdm$my_cohort |>
  newCohortTable(
    cohortSetRef = cohort_set, # table with the settings of the cohort_table
    cohortAttritionRef = cohort_attrition, # table with the attrition of the cohort_table
    cohortCodelistRef = cohort_codelist # table with the codelists of the cohort_table
  )

This step can be included in your cdm object creation if you wish:

cdmFromMyCustomSource <- function(argument1, argument2, ..., cohortTables) {
  # read and prepare the cdm tables
  ...
  
  # return the cdm object
  cdm <- omopgenerics::newCdmReference(
    tables = tables, # list of cdm and achilles standard tables
    cdmName = "...", # usually provided as input, but also you might want to search in the cdm_source
    cdmVersion = "..." # either "5.3" or "5.4"
  )
  
  # read cohort tables
  readSourceTable(cdm = cdm, name = cohortTables)
}

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