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我有一个shiny应用程序RPostgreSQL用于连接到数据库并临时查询数据。

# Initialize environment to hold SQL parameters:
library(RPostgreSQL)
if (!exists('.sql')) .sql <- new.env()
.sql$cxn <- dbConnect(PostgreSQL(), host = "localhost", dbname = "testdb", user = "myuser", password = "Passw0rd!", port = 5432)

此代码在应用程序初始化时运行，但一段时间后，连接被服务器终止：

> dbGetQuery(.sql$cxn, "SELECT 1")
Error in postgresqlExecStatement(conn, statement, ...) : 
  RS-DBI driver: (could not run statement: no connection to the server
)

如果我只是打电话：

.sql$cxn <- dbConnect(PostgreSQL(), host = "localhost", dbname = "testdb", user = "myuser", password = "Passw0rd!", port = 5432)

再次，它创建了第二个连接：（我不希望这样）

> dbListConnections(PostgreSQL())
[[1]]
<PostgreSQLConnection:(10601,4)> 

[[2]]
<PostgreSQLConnection:(10601,5)>

（最终，已达到最大连接数，您无法创建另一个：https ://groups.google.com/forum/#!topic/shiny-discuss/0VjQc2a6z3M ）

我想创建一个连接到我的 PostgreSQL 数据库的函数（如果它还没有），并保持连接打开（通过 SELECT'ing 1）如果它有：

getConnection <- function(.host, .user, .pw) {
  tryCatch({
    if (!exists('cxn', where = .sql)) {
      .sql$cxn <- dbConnect(PostgreSQL(), host = .host, dbname = "testdb", user = .user, password = .pw, port = 5432)
    } else {
      dbGetQuery(.sql$cxn, "SELECT 1")
    }
  }, warning = function(w) {
    NULL  # placeholder for warnings
  }, error = function(e) {
    print(e)
    cat("Looks like PostgreSQL connection died. Let's try to reconnect...\n")
    invisible(lapply(dbListConnections(PostgreSQL()), dbDisconnect))  # Close all db connections
.sql$cxn <<- dbConnect(PostgreSQL(), host = .host, dbname = "testdb", user = .user, password = .pw, port = 5432)
  }, finally = {
    return(.sql$cxn)
  })
}

getConnection(.host = "localhost", .user = "myuser", .pw = "Passw0rd!")

编辑 2016/03/12：不知道为什么，但我上面写的函数似乎不能正常工作......

当我调用它时，我得到：

> getConnection(.host = awsrds$host, .user = awsrds$username, .pw = awsrds$password)
Error in postgresqlExecStatement(conn, statement, ...) : 
  RS-DBI driver: (could not run statement: no connection to the server
)
<PostgreSQLConnection:(12495,0)>

特别是，这部分dbGetQuery(.sql$cxn, "SELECT 1")返回：

Error in postgresqlExecStatement(conn, statement, ...) : 
  RS-DBI driver: (could not run statement: no connection to the server
)
NULL
Warning message:
In postgresqlQuickSQL(conn, statement, ...) :
  Could not create executeSELECT 1

这个class输出是NULL（而不是错误？）。

任何想法我做错了什么？谢谢！

4

1 回答 1

-2

我相信您可以通过在您的连接功能中包含检查来解决该错误。这就是我为 mysql 所做的......我相信在你的情况下应该工作相同。关键是检查是否SELECT 1 == 'try-error'

connectionFunction <- function() {
  if (!exists("connectionName", where = .GlobalEnv)) {
      connectionName <<- dbConnect(MySQL(), default.file = mysqlconf, dbname = "dbName")
  } else if (class(try(dbGetQuery(connectionName, "SELECT 1"))) == "try-error") {
      dbDisconnect(connectionName)
      connectionName <<- dbConnect(MySQL(), default.file = mysqlconf, dbName = "dbName")
  }
  return(connectionName)

}

于 2016-03-01T15:30:48.763 回答