6

我正在使用 R 包 dbplyr 创建一个数据库，使用 RSQLite，但是尽管我写（和读回）一个表，但我的数据库在磁盘上的大小是零字节。这是我的脚本：

library("RSQLite")
library("dbplyr")
library("dplyr")

data(mtcars)

con <- DBI::dbConnect(RSQLite::SQLite(), dbname = "./mtcars.db")
copy_to(con, mtcars, "mtcars")

print(tbl(con, "mtcars"))

但是正如您从最后的 ls -l 中看到的那样，我的数据库大小为 0，即使脚本确实从数据库中读取了 mtcars（所以它就在那里）。我想使用数据库文件与另一个程序共享数据，那么如何定期将数据“刷新”到磁盘？

tbrowne@calculon:~/scratch$ R -f dplysqlite.r 

R version 3.2.3 (2015-12-10) -- "Wooden Christmas-Tree"
Copyright (C) 2015 The R Foundation for Statistical Computing
Platform: x86_64-pc-linux-gnu (64-bit)

R is free software and comes with ABSOLUTELY NO WARRANTY.
You are welcome to redistribute it under certain conditions.
Type 'license()' or 'licence()' for distribution details.

  Natural language support but running in an English locale

R is a collaborative project with many contributors.
Type 'contributors()' for more information and
'citation()' on how to cite R or R packages in publications.

Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.

> 
> library("RSQLite")
> library("dbplyr")
Warning messages:
1: replacing previous import by ‘rlang::enquo’ when loading ‘dbplyr’ 
2: replacing previous import by ‘rlang::quo’ when loading ‘dbplyr’ 
3: replacing previous import by ‘rlang::quos’ when loading ‘dbplyr’ 
4: replacing previous import by ‘rlang::quo_name’ when loading ‘dbplyr’ 
> library("dplyr")

Attaching package: ‘dplyr’

The following objects are masked from ‘package:dbplyr’:

    ident, sql

The following objects are masked from ‘package:stats’:

    filter, lag

The following objects are masked from ‘package:base’:

    intersect, setdiff, setequal, union

> 
> data(mtcars)
> 
> con <- DBI::dbConnect(RSQLite::SQLite(), dbname = "./mtcars.db")
> copy_to(con, mtcars, "mtcars")
> 
> print(tbl(con, "mtcars"))
# Source:   table<mtcars> [?? x 11]
# Database: sqlite 3.19.3 [/home/tbrowne/scratch/mtcars.db]
     mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb
   <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
 1  21.0     6 160.0   110  3.90 2.620 16.46     0     1     4     4
 2  21.0     6 160.0   110  3.90 2.875 17.02     0     1     4     4
 3  22.8     4 108.0    93  3.85 2.320 18.61     1     1     4     1
 4  21.4     6 258.0   110  3.08 3.215 19.44     1     0     3     1
 5  18.7     8 360.0   175  3.15 3.440 17.02     0     0     3     2
 6  18.1     6 225.0   105  2.76 3.460 20.22     1     0     3     1
 7  14.3     8 360.0   245  3.21 3.570 15.84     0     0     3     4
 8  24.4     4 146.7    62  3.69 3.190 20.00     1     0     4     2
 9  22.8     4 140.8    95  3.92 3.150 22.90     1     0     4     2
10  19.2     6 167.6   123  3.92 3.440 18.30     1     0     4     4
# ... with more rows
> 
> 
tbrowne@calculon:~/scratch$ ls -l
total 4
-rw-rw-r-- 1 tbrowne tbrowne 194 Oct 31 11:04 dplysqlite.r
-rw-r--r-- 1 tbrowne tbrowne   0 Oct 31 11:04 mtcars.db
4

2 回答 2

6

您没有使用RSQLite文档建议的模式。该文档用于dbWriteTable将数据框复制到 SQLite 表中：

dbWriteTable(con, "mtcars", mtcars)

根据此文档，您的完整代码将如下所示：

con <- dbConnect(RSQLite::SQLite(), "./mtcars.db")
data(mtcars)
dbWriteTable(con, "mtcars", mtcars)
dbListTables(con)
# Fetch all query results into a data frame:
dbGetQuery(con, "SELECT * FROM mtcars")
于 2017-10-31T11:25:24.387 回答
6

copy_to()dbplyr 源 ( dbplyr:::copy_to.src_sql())的方法有一个默认temporary设置为的参数。TRUE这意味着新表将仅对您的活动连接可见，并在您关闭连接后消失。以下应该按预期工作：

copy_to(con, mtcars, "mtcars", temporary = FALSE)

或者，dbWriteTable()按照 Tim 的建议使用。

于 2017-11-01T09:44:32.887 回答