SQLite

** implementation takes care of opening and closing database files
** automatically.
**
** UNIONVTAB
**
**   A "unionvtab" virtual table is created as follows:
**
**     CREATE VIRTUAL TABLE <name> USING unionvtab(<sql-statement>);
**
**   The implementation evalutes <sql statement> whenever a unionvtab virtual
**   table is created or opened. It should return one row for each source
**   database table. The four columns required of each row are:
**
**     1. The name of the database containing the table ("main" or "temp" or
**        the name of an attached database). Or NULL to indicate that all

**     4. The largest rowid in the range of rowids that may be stored in the
**        database table (an integer).
**
** SWARMVTAB
**
**   A "swarmvtab" virtual table is created similarly to a unionvtab table:
**
**     CREATE VIRTUAL TABLE <name>
**      USING swarmvtab(<sql-statement>, <callback>);
**
**   The difference is that for a swarmvtab table, the first column returned
**   by the <sql statement> must return a path or URI that can be used to open
**   the database file containing the source table.  The <callback> option
**   is optional.  If included, it is the name of an application-defined
**   SQL function that is invoked with the URI of the file, if the file
**   does not already exist on disk.
*/

#include "sqlite3ext.h"
SQLITE_EXTENSION_INIT1
#include <assert.h>
#include <string.h>

  int bSwarm;                     /* 1 for "swarmvtab", 0 for "unionvtab" */
  int iPK;                        /* INTEGER PRIMARY KEY column, or -1 */
  int nSrc;                       /* Number of elements in the aSrc[] array */
  UnionSrc *aSrc;                 /* Array of source tables, sorted by rowid */

  /* Used by swarmvtab only */
  char *zSourceStr;               /* Expected unionSourceToStr() value */
  char *zNotFoundCallback;        /* UDF to invoke if file not found on open */
  UnionSrc *pClosable;            /* First in list of closable sources */
  int nOpen;                      /* Current number of open sources */
  int nMaxOpen;                   /* Maximum number of open sources */
};

/*
** Virtual table cursor type for union vtab.

      UnionSrc *pSrc = &pTab->aSrc[i];
      sqlite3_free(pSrc->zDb);
      sqlite3_free(pSrc->zTab);
      sqlite3_free(pSrc->zFile);
      sqlite3_close(pSrc->db);
    }
    sqlite3_free(pTab->zSourceStr);
    sqlite3_free(pTab->zNotFoundCallback);
    sqlite3_free(pTab->aSrc);
    sqlite3_free(pTab);
  }
  return SQLITE_OK;
}

/*

    sqlite3_free(z);
  }
  sqlite3_free(z0);

  return rc;
}


/*
** Try to open the swarmvtab database.  If initially unable, invoke the
** not-found callback UDF and then try again.
*/
static int unionOpenDatabaseInner(UnionTab *pTab, UnionSrc *pSrc, char **pzErr){
  int rc = SQLITE_OK;
  static const int openFlags = 
       SQLITE_OPEN_READONLY | SQLITE_OPEN_URI;
  rc = sqlite3_open_v2(pSrc->zFile, &pSrc->db, openFlags, 0);
  if( rc==SQLITE_OK ) return rc;
  if( pTab->zNotFoundCallback ){
    char *zSql = sqlite3_mprintf("SELECT \"%w\"(%Q);",
                    pTab->zNotFoundCallback, pSrc->zFile);
    if( zSql==0 ){
      *pzErr = sqlite3_mprintf("out of memory");
      return SQLITE_NOMEM;
    }
    rc = sqlite3_exec(pTab->db, zSql, 0, 0, pzErr);
    sqlite3_free(zSql);
    if( rc ) return rc;
    rc = sqlite3_open_v2(pSrc->zFile, &pSrc->db, openFlags, 0);
  }
  if( rc!=SQLITE_OK ){
    *pzErr = sqlite3_mprintf("%s", sqlite3_errmsg(pSrc->db));
  }
  return rc;
}

/*
** This function may only be called for swarmvtab tables. The results of
** calling it on a unionvtab table are undefined.
**
** For a swarmvtab table, this function ensures that source database iSrc
** is open. If the database is opened successfully and the schema is as
** expected, or if it is already open when this function is called, SQLITE_OK

static int unionOpenDatabase(UnionTab *pTab, int iSrc, char **pzErr){
  int rc = SQLITE_OK;
  UnionSrc *pSrc = &pTab->aSrc[iSrc];

  assert( pTab->bSwarm && iSrc<pTab->nSrc );
  if( pSrc->db==0 ){
    unionCloseSources(pTab, pTab->nMaxOpen-1);
    rc = unionOpenDatabaseInner(pTab, pSrc, pzErr);
    if( rc==SQLITE_OK ){


      char *z = unionSourceToStr(&rc, pTab, pSrc, pzErr);
      if( rc==SQLITE_OK ){
        if( pTab->zSourceStr==0 ){
          pTab->zSourceStr = z;
        }else{
          if( sqlite3_stricmp(z, pTab->zSourceStr) ){
            *pzErr = sqlite3_mprintf("source table schema mismatch");

}

/* 
** xConnect/xCreate method.
**
** The argv[] array contains the following:
**
**   argv[0]   -> module name  ("unionvtab" or "swarmvtab")
**   argv[1]   -> database name
**   argv[2]   -> table name
**   argv[3]   -> SQL statement
**   argv[4]   -> not-found callback UDF name
*/
static int unionConnect(
  sqlite3 *db,
  void *pAux,
  int argc, const char *const*argv,
  sqlite3_vtab **ppVtab,
  char **pzErr
){
  UnionTab *pTab = 0;
  int rc = SQLITE_OK;
  int bSwarm = (pAux==0 ? 0 : 1);
  const char *zVtab = (bSwarm ? "swarmvtab" : "unionvtab");

  if( sqlite3_stricmp("temp", argv[1]) ){
    /* unionvtab tables may only be created in the temp schema */
    *pzErr = sqlite3_mprintf("%s tables must be created in TEMP schema", zVtab);
    rc = SQLITE_ERROR;
  }else if( argc!=4 && argc!=5 ){
    *pzErr = sqlite3_mprintf("wrong number of arguments for %s", zVtab);
    rc = SQLITE_ERROR;
  }else{
    int nAlloc = 0;               /* Allocated size of pTab->aSrc[] */
    sqlite3_stmt *pStmt = 0;      /* Argument statement */
    char *zArg = unionStrdup(&rc, argv[3]);      /* Copy of argument to CVT */

        }else{
          pSrc->zDb = unionStrdup(&rc, zDb);
        }
      }
    }
    unionFinalize(&rc, pStmt, pzErr);
    pStmt = 0;

    /* Capture the not-found callback UDF name */
    if( argc>=5 ){
      pTab->zNotFoundCallback = unionStrdup(&rc, argv[4]);
      unionDequote(pTab->zNotFoundCallback);
    }

    /* It is an error if the SELECT statement returned zero rows. If only
    ** because there is no way to determine the schema of the virtual 
    ** table in this case.  */
    if( rc==SQLITE_OK && pTab->nSrc==0 ){
      *pzErr = sqlite3_mprintf("no source tables configured");
      rc = SQLITE_ERROR;

# 2017-07-15
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this file is the "swarmvtab" extension
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
set testprefix swarmvtab

ifcapable !vtab {
  finish_test
  return
}


db close
foreach name [glob -nocomplain test*.db] {
  forcedelete $name
}
sqlite3 db test.db
load_static_extension db unionvtab
proc create_database {filename} {
  sqlite3 dbx $filename
  set num [regsub -all {[^0-9]+} $filename {}]
  set num [string trimleft $num 0]
  set start [expr {$num*1000}]
  set end [expr {$start+999}]
  dbx eval {
    CREATE TABLE t2(a INTEGER PRIMARY KEY,b);
    WITH RECURSIVE c(x) AS (
      VALUES($start) UNION ALL SELECT x+1 FROM c WHERE x<$end
    )
    INSERT INTO t2(a,b) SELECT x, printf('**%05d**',x) FROM c;
  }
  dbx close
}
db func create_database create_database
do_execsql_test 100 {
  CREATE TABLE t1(filename, tablename, istart, iend);
  WITH RECURSIVE c(x) AS (VALUES(1) UNION ALL SELECT x+1 FROM c WHERE x<99)
  INSERT INTO t1 SELECT printf('test%03d.db',x),'t2',x*1000,x*1000+999 FROM c;
  CREATE VIRTUAL TABLE temp.v1 USING swarmvtab(
    'SELECT * FROM t1', 'create_database'
  );
} {}
do_execsql_test 110 {
  SELECT b FROM v1 WHERE a=3875;
} {**03875**}
do_test 120 {
  lsort [glob -nocomplain test?*.db]
} {test001.db test003.db}
do_execsql_test 130 {
  SELECT b FROM v1 WHERE a BETWEEN 3999 AND 4000 ORDER BY a;
} {**03999** **04000**}
do_test 140 {
  lsort [glob -nocomplain test?*.db]
} {test001.db test003.db test004.db}
do_execsql_test 150 {
  SELECT b FROM v1 WHERE a>=99998;
} {**99998** **99999**}
do_test 160 {
  lsort -dictionary [glob -nocomplain test?*.db]
} {test001.db test003.db test004.db test099.db}

finish_test