The Database Module - Tcl

This page contains the explanations, usage, and syntax of the methods and the configurable parameters for the DBase object class.

Methods

<object> puts
<object> list
List all the keys of the of the data base. Just entering the name of the object has the same behaviour as calling the puts method.
<object> read <filename>
Read entries from the named file. The lines in the file are added to the entries that are already in the given object. Entries with the same key are overwritten. The old entry is removed and the new entry is added. (This does most likely change the sequence of entries, which means that the first and next methods will return their results in a different order.
<object> write <filename>
Expects one argument, the name of the file into which it should write the (human readable) entries of the given object.
<object> add <key> <value>
Expects a string (the key of the entry) and a second string (the value for this key). These form the entry that will be added to the database. Already existing entries with the same key are overwritten. The old entry is removed and the new entry is added. (This does most likely change the sequence of entries, which means that the first and next methods will return their results in a different order.
<object> delete <key>
Expects the name of a key, which will be removed from the database.
<object> get <key>
Expects the name of a key, whose value will be returned. If you are using a list of two element lists, you can do makeArray arr [dbase get $key] which will give you an array where arr(variable) returns the second element of the two-elment list whose first element is variable.
<object> first <>
<object> next <>
first returns the first key of the database, and next returns the next key. So you can write a loop over all entries like this:
```
for { set x [dbase first] } { [string length $x] } { set x [dbase next] } { ... }
```

Accessing Subobjects

The DBase object has one subobject that is created automatically, a DBaseIdx type object. From Tcl, you can't do much with a single DBaseIdx. From C it can be used for creating custom type databases. The only thing you'll need it from Tcl, is to set the size of the key hash-table.

Configurable Parameters

The DBaseIdx class has one configurable parameter, which is:

-hashSizeX <integer>
the power of two, defining the size of the hash table. A good size is slightly more than the number of items you want to store in the database. So if you want to store 80000 items you'd pobably set -hashSizeX to 17, because 2 to the 17th is more than 80000 and 2 to the 16th is less. Chosing a too small hash table will not keep your database from working, it just might be very slow.