CREATE FROM

CREATE FROM

Create new database file from a structure extended file

Syntax

      CREATE <xcFileName> FROM <xcFileFrom> [VIA <xcRDDName>];
              [NEW] [ALIAS <xcAlias>]

Arguments

<xcFileName&gt : is the target file name to create and then open. (.dbf) is the default extension if none is given. It can be specified as literal file name or as a character expression enclosed in parentheses.

<FROM xcFileFrom> : is a structure extended file name from which the target file <xcFileName> is going to be built. It can be specified as literal file name or as a character expression enclosed in parentheses.

<VIA xcRDDName> : is RDD name to create target with. If omitted, the default RDD is used. It can be specified as literal name or as a character expression enclosed in parentheses.

<NEW> : open the target file name <xcFileName> in the next available unused work-area and making it the current work-area. If omitted open the target file in current work-area.

<ALIAS xcAlias>  :  is an optional alias to USE the target file with. If not specified, alias is based on the root name of <xcFileName>.

Description

CREATE FROM open a structure extended file <xcFileFrom> where each record contain at least the following fields (in no particular order): FIELD_NAME, FIELD_TYPE, FIELD_LEN and FIELD_DEC. Any other field is ignored. From this information the file <xcFileName> is then created and opened in the current or new work-area (according to the NEW clause), if this is a new work-area it becomes the current.

For prehistoric compatibility reasons, structure extended file Character fields which are longer than 255 characters should be treated in a special way by writing part of the length in the FIELD_DEC according to the following formula:

      FIELD->FIELD_DEC := int( nLength / 256 )
      FIELD->FIELD_LEN := ( nLength % 256 )

CREATE FROM command is preprocessed into __dbCopyStruct() function during compile time and uses this mode.

Examples

      See example in the CREATE command

Compliance

Clipper

Platforms

All

Seealso

COPY STRUCTURE, COPY STRUCTURE EXTENDED, CREATE, DBCREATE(), DBSTRUCT(), __dbCopyStruct(), __dbCopyXStruct(), __dbCreate()

CREATE

 

CREATE

Create empty structure extended file

Syntax

      CREATE <xcFileName> [VIA <xcRDDName>] [ALIAS <xcAlias>]

Arguments

<xcFileName> : is the target file name to create and then open. (.dbf) is the default extension if none is given. It can be specified as literal file name or as a character expression enclosed in parentheses.

<VIA xcRDDName> :is RDD name to create target with. If omitted, the default RDD is used. It can be specified as literal name or as a character expression enclosed in parentheses.

<ALIAS xcAlias> : is an optional alias to USE the target file with. If not specified, alias is based on the root name of <xcFileName>.

Description

CREATE a new empty structure extended file with the name <cFileName> and then open it in the current work-area. The new file has the following structure:

       Field name   Type   Length   Decimals
       ------------ ----   ------   --------
       FIELD_NAME   C      10       0
       FIELD_TYPE   C      1        0
       FIELD_LEN    N      3        0
       FIELD_DEC    N      3        0

CREATE command is preprocessed into __dbCopyStruct() function during compile time and use this mode.

Examples

      // CREATE a new structure extended file, append some records and
      // then CREATE FROM this file a new database file

      CREATE template
      APPEND BLANK
      FIELD->FIELD_NAME := "CHANNEL"
      FIELD->FIELD_TYPE := "N"
      FIELD->FIELD_LEN  := 2
      FIELD->FIELD_DEC  := 0
      APPEND BLANK
      FIELD->FIELD_NAME := "PROGRAM"
      FIELD->FIELD_TYPE := "C"
      FIELD->FIELD_LEN  := 20
      FIELD->FIELD_DEC  := 0
      APPEND BLANK
      FIELD->FIELD_NAME := "REVIEW"
      FIELD->FIELD_TYPE := "C"      // this field is 1000 char long
      FIELD->FIELD_LEN  := 232      // 1000 % 256 = 232
      FIELD->FIELD_DEC  := 3        // 1000 / 256 = 3
      CLOSE
      CREATE TV_Guide FROM template

Compliance

Clipper

Platforms

All

Seealso

COPY STRUCTURE, COPY STRUCTURE EXTENDED, CREATE FROM, DBCREATE(), DBSTRUCT(), __dbCopyStruct(), __dbCopyXStruct(), __dbCreate()

COPY STRUCTURE EXTENDED

COPY STRUCTURE EXTENDED

Copy current database structure into a definition file

Syntax

      COPY STRUCTURE EXTENDED TO <xcFileName>

Arguments

<xcFileName> The name of the target definition file to create. (.dbf) is the default extension if none is given. It can be specified as a literal file name or as a character expression enclosed in parentheses.

Description

COPY STRUCTURE EXTENDED create a new database named <cFileName> with a pre-defined structure (also called “structure extended file” ) :

       Field name   Type   Length   Decimals
       -----------  ----   ------   ---------  
       FIELD_NAME   C      10       0
       FIELD_TYPE   C      1        0
       FIELD_LEN    N      3        0
       FIELD_DEC    N      3        0

Each record in the new file contains information about one field in the original file. CREATE FROM could be used to create a database from the structure extended file.

For prehistoric compatibility reasons, Character fields which are longer than 255 characters are treated in a special way by writing part of the length in the FIELD_DEC according to the following formula (this is done internally) :

      FIELD->FIELD_DEC := int( nLength / 256 ) 
      FIELD->FIELD_LEN := ( nLength % 256 )

Later if you want to calculate the length of a field you can use the following formula:

      nLength := iif( FIELD->FIELD_TYPE == "C", ;
                      FIELD->FIELD_DEC * 256 + FIELD->FIELD_LEN, ;
                      FIELD->FIELD_LEN )

COPY STRUCTURE EXTENDED command is preprocessed into __dbCopyXStruct() function during compile time.

Examples

      // Open a database, then copy its structure to a new file,
      // Open the new file and list all its records
      USE Test
      COPY STRUCTURE EXTENDED TO TestStru
      USE TestStru
      LIST

Compliance

Clipper

Platforms

All

Seealso

COPY STRUCTURE, CREATE, CREATE FROM, DBCREATE(), DBSTRUCT(), __dbCopyStruct(), __dbCopyXStruct(), __dbCreate()

COPY STRUCTURE

 

COPY STRUCTURE

Create a new database based on current database structure

Syntax

      COPY STRUCTURE TO <xcFileName> [FIELDS <field,...>]

Arguments

TO <xcFileName> is the name of the new database file to create. (.dbf) is the default extension if none is given. It can be specified as a literal file name or as a character expression enclosed in parentheses.

FIELDS <field, …> is an optional list of field names to copy from the currently open database in the specified order, the default is all fields. Names could be specified as uppercase or lowercase.

Description

COPY STRUCTURE create a new empty database file with a structure that is based on the currently open database in this work-area.

COPY STRUCTURE can be use to create a sub-set of the currently open database, based on a given field list.

COPY STRUCTURE command is preprocessed into __dbCopyStruct() function during compile time.

Examples

      // Create a new file that contains the same structure
       USE TEST
       COPY STRUCTURE TO MyCopy

       // Create a new file that contains part of the original structure
       USE TEST
       COPY STRUCTURE TO SomePart FIELDS name, address

Compliance

Clipper

Platforms

All

Seealso

COPY STRUCTURE EXTENDED, DBCREATE(), DBSTRUCT(), __dbCopyStruct(), __dbCopyXStruct(), __dbCreate(), __dbStructFilter()

__FLedit()

Template

Function

Name

__FLedit()*

Category

API

Subcategory

Database

Oneliner

Filter a database structure array

Syntax

      __FLedit( <aStruct>,  [<aFieldList>] ) --> aStructFiltered

Arguments

<aStruct> is a multidimensional array with database fields structure, which is usually the output from dbStruct(), where each array element has the following structure:

       Position   Description    dbstruct.ch
       --------   -----------    -----------
       1          cFieldName     DBS_NAME
       2          cFieldType     DBS_TYPE
       3          nFieldLength   DBS_LEN
       4          nDecimals      DBS_DEC

<aFieldList> is an array where each element is a field name. Names could be specified as uppercase or lowercase.

Returns

__FLedit() return a new multidimensional array where each element is in the same structure as the original <aStruct>, but the array is built according to the list of fields in <aFieldList>. If <aFieldList> is empty, __FLedit() return reference to the original <aStruct> array.

Description

__FLedit() can be use to create a sub-set of a database structure, based on a given field list.

Note that field names in <aStruct> MUST be specified in uppercase or else no match would found.

SET EXACT has no effect on the return value.

__FLedit() is a compatibility function and it is synonym for __dbStructFilter() which does exactly the same.

Examples

      LOCAL aStruct,  aList,  aRet
      aStruct := { { "CODE",   "N",   4,  0 },  ;
                   { "NAME",   "C",  10,  0 },  ;
                   { "PHONE",  "C",  13,  0 },  ;
                   { "IQ",     "N",   3,  0 } }
      aList := { "IQ",  "NAME" }
      aRet := __FLedit( aStruct,  aList )
                        // { { "IQ",  "N",  3,  0 },  { "NAME",  "C",  10,  0 } }

      aRet := __FLedit( aStruct,  {} )
      ? aRet == aStruct // .T.

      aList := { "iq",  "NOTEXIST" }
      aRet := __FLedit( aStruct,  aList )
                        // { { "IQ",  "N",  3,  0 } }

      aList := { "NOTEXIST" }
      aRet := __FLedit( aStruct,  aList )   // {}

      // Create a new file that contain part of the original structure
      LOCAL aStruct,  aList,  aRet
      USE TEST
      aStruct := dbStruct()
      aList := { "NAME" }
      dbCreate( "onlyname.dbf",  __FLedit( aStruct,  aList ) )

Compliance

CA-Cl*pper has internal undocumented function named __FLedit(), in Harbour we name it __dbStructFilter(). The new name gives a better description of what this function does. In Harbour __FLedit() simply calls __dbStructFilter() and therefor the latter is the recommended function to use.

This function is only visible if src/rdd/dbstrux.prg was compiled with the HB_CLP_UNDOC flag.

Platforms

All

Files

Header file is dbstruct.ch
Library is rdd

Seealso

dbCreate(), dbStruct(), __dbCopyStruct(), __dbStructFilter()

__dbStructFilter()

Template

Function

Name

__dbStructFilter()

Category

API

Subcategory

Database

Oneliner

Filter a database structure array

Syntax

      __dbStructFilter( <aStruct>,  [<aFieldList>] ) --> aStructFiltered

Arguments

<aStruct> is a multidimensional array with database fields structure, which is usually the output from dbStruct(), where each array element has the following structure:

       Position   Description    dbstruct.ch
       --------   -----------    -----------
       1          cFieldName     DBS_NAME
       2          cFieldType     DBS_TYPE
       3          nFieldLength   DBS_LEN
       4          nDecimals      DBS_DEC

<aFieldList> is an array where each element is a field name. Names could be specified as uppercase or lowercase.

Returns

__dbStructFilter() return a new multidimensional array where each element is in the same structure as the original <aStruct>, but the array is built according to the list of fields in <aFieldList>. If <aFieldList> is empty, __dbStructFilter() return reference to the original <aStruct> array.

Description

__dbStructFilter() can be use to create a sub-set of a database structure, based on a given field list.

Note that field names in <aStruct> MUST be specified in uppercase or else no match would be found.

SET EXACT has no effect on the return value.

Examples

      LOCAL aStruct,  aList,  aRet
      aStruct := { ;
         { "CODE",   "N",   4,  0 },  ;
         { "NAME",   "C",  10,  0 },  ;
         { "PHONE",  "C",  13,  0 },  ;
         { "IQ",     "N",   3,  0 } }
      aList := { "IQ",  "NAME" }
      aRet := __dbStructFilter( aStruct,  aList )
                        // { { "IQ",  "N",  3,  0 },  { "NAME",  "C",  10,  0 } }

      aRet := __dbStructFilter( aStruct,  {} )
      ? aRet == aStruct // .T.

      aList := { "iq",  "NOTEXIST" }
      aRet := __dbStructFilter( aStruct,  aList )
                        // { { "IQ",  "N",  3,  0 } }

      aList := { "NOTEXIST" }
      aRet := __dbStructFilter( aStruct,  aList )   // {}

      // Create a new file that contain part of the original structure
      LOCAL aStruct,  aList,  aRet
      USE TEST
      aStruct := dbStruct()
      aList := { "NAME" }
      dbCreate( "onlyname.dbf",  __dbStructFilter( aStruct,  aList ) )

Compliance

__dbStructFilter() is a Harbour extension. CA-Cl*pper has an internal undocumented function named __FLedit() that does exactly the same thing. The new name gives a better description of what this  function does.

Platforms

All

Files

Header file is dbstruct.ch
Library is rdd

Seealso

dbCreate(), dbStruct(), __dbCopyStruct(), __FLedit()*

__dbCreate()

Template

Function

Name

__dbCreate()

Category

API

Subcategory

Database

Oneliner

Create structure extended file or use one to create new file

Syntax

      __dbCreate( <cFileName>,  [<cFileFrom>],  [<cRDDName>],  ;
                  [<lNew>],  [<cAlias>] ) --> lUsed

Arguments

<cFileName> is the target file name to create and then open. (.dbf) is the default extension if none is given.

<cFileFrom> is an optional structure extended file name from which the target file <cFileName> is going to be built. If omitted, a new empty structure extended file with the name <cFileName> is created and opened in the current work-area.

<cRDDName> is RDD name to create target with. If omitted, the default RDD is used.

<lNew> is an optional logical expression, (.T.) opens the target file name <cFileName> in the next available unused work-area and makes it the current work-area. (.F.) opens the target file in the current
work-area. Default value is (.F.). The value of <lNew> is ignored if <cFileFrom> is not specified.

<cAlias> is an optional alias to USE the target file with. If not specified, alias is based on the root name of <cFileName>.

Returns

__dbCreate() returns (.T.) if there is database USED in the current work-area (this might be the newly selected work-area), or (.F.) if there is no database USED. Note that on success a (.T.) would be returned, but on failure you probably end up with a run-time error and not a (.F.) value.

Description

__dbCreate() works in two modes depending on the value of <cFileFrom>:

1) If <cFileFrom> is empty or not specified a new empty structure extended file with the name <cFileName> is created and then opened in the current work-area (<lNew> is ignored). The new
file has the following structure:

       Field name   Type   Length   Decimals
       ----------   ----   ------   --------
       FIELD_NAME   C      10        0
       FIELD_TYPE   C       1        0
       FIELD_LEN    N       3        0
       FIELD_DEC    N       3        0

The CREATE command is preprocessed into the __dbCopyStruct() function during compile time and uses this mode.

2) If <cFileFrom> is specified, it is opened and assumed to be a structure extended file where each record contains at least the following fields (in no particular order): FIELD_NAME, FIELD_TYPE,
FIELD_LEN and FIELD_DEC. Any other field is ignored. From this information the file <cFileName> is then created and opened in the current or new work-area (according to <lNew>), if this is a new work-area it becomes the current.

For prehistoric compatibility reasons, structure extended file Character fields which are longer than 255 characters should be treated in a special way by writing part of the length in the FIELD_DEC according to the following formula:

      FIELD->FIELD_DEC := Int( nLength / 256 )
      FIELD->FIELD_LEN := ( nLength % 256 )

CREATE FROM command is preprocessed into __dbCopyStruct() function during compile time and use this mode.

Examples

      // CREATE a new structure extended file,  append some records and
      // then CREATE FROM this file a new database file

      __dbCreate( "template" )
      dbAppend()
      FIELD->FIELD_NAME := "CHANNEL"
      FIELD->FIELD_TYPE := "N"
      FIELD->FIELD_LEN  := 2
      FIELD->FIELD_DEC  := 0
      dbAppend()
      FIELD->FIELD_NAME := "PROGRAM"
      FIELD->FIELD_TYPE := "C"
      FIELD->FIELD_LEN  := 20
      FIELD->FIELD_DEC  := 0
      dbAppend()
      FIELD->FIELD_NAME := "REVIEW"
      FIELD->FIELD_TYPE := "C"      // this field is 1000 char long
      FIELD->FIELD_LEN  := 232      // 1000 % 256 = 232
      FIELD->FIELD_DEC  := 3        // 1000 / 256 = 3
      dbCloseArea()
      __dbCreate( "TV_Guide",  "template" )

Compliance

Clipper

Platforms

All

Files

Library is rdd

Seealso

COPY STRUCTURE, COPY STRUCTURE EXTENDED, CREATE, CREATE FROM, dbCreate(), dbStruct(), __dbCopyStruct(), __dbCopyXStruct()