如何将数据“刷新”到我的 RSQLite 磁盘数据库？

Question

我正在使用 R 包 dbplyr 创建一个数据库，使用 RSQLite，但我的数据库在磁盘上的大小为零字节，尽管我写了（和读回）了一个表。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"))

但是正如你从最后的 ls -l 看到的，我的数据库大小是 0，即使脚本确实从数据库中读取了 mtcars（所以它在那里）。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 

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> 
> 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

Answer 1

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")

Answer 2

copy_to()dbplyr 源 ( dbplyr:::copy_to.src_sql())的方法有一个默认temporary设置为TRUE的参数。这意味着新表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。