Exploring dbplyr

lazy-explore.R

# create database connection
con <- dbConnect(...)

# define tbl object
mytbl <- tbl(con, "table")

# dbplyr:::tbl_sql
# -> op_base_remote
# --> get list of var names (by doing a quick query)
# --> op_base
# ----> STORES vars, "op_base_remote" tag
# dplyr::make_tbl

mytbl1 <- mytbl %>% filter(column > 2)
# dbplyr:::filter.tbl_lazy
# -> quos(...)
# -> partial_eval_dots(dots, vars = op_vars(.data))
# -> add_op_single("filter", .data, dots = dots)

mytbl2 <- mytbl1 %>% mutate(column2 = "a")
# dbplyr:::mutate.tbl_lazy
# -> dots <- quos(..., .named = TRUE)
# -> dots <- partial_eval_dots(dots, vars = op_vars(.data))
# -> nest_vars(.data, dots, union(op_vars(.data), op_grps(.data)))

mytbl2
# dbplyr:::print.tbl_sql
# -> cat_line(format(...))
# --> tibble:::format.tbl
# --> tibble:::trunc_mat
# ---> as.data.frame(head(x, n))
# ---> dbplyr:::head.tbl_lazy
# ----> op_single("head", x = x$ops, args = list(n = n))
# ---> dbplyr:::as.data.frame.tbl_sql
# ----> as.data.frame(collect(x, n = n))
# ----> dbplyr:::collect.tbl_sql
# -----> dbplyr:::db_sql_render
# -----> dbplyr:::db_collect