Class: LMDB::Database

Inherits:
Object
  • Object
show all
Includes:
Enumerable
Defined in:
ext/lmdb_ext/lmdb_ext.c,
lib/lmdb/database.rb,
ext/lmdb_ext/lmdb_ext.c

Overview

An LMDB Database is a table of key-value pairs. It is stored as part of the Environment.

By default, each key in a Database maps to one value. However, a Database can be configured at creation to allow duplicate keys, in which case one key will map to multiple values.

A Database stores the keys in a sorted order. The order can also be set with options when the database is created.

The basic operations on a database are to #put, #get, and #delete records. One can also iterate through the records in a database using a Cursor.

Examples:

Typical usage

env = LMDB.new "databasedir"
db = env.database "databasename"
db.put "key1", "value1"
db.put "key2", "value2"
db.get "key1"              #=> "value1"
env.close

Instance Method Summary collapse

Instance Method Details

#[](key) ⇒ Object

Retrieve the value of a record from a database

Parameters:

  • key —

    the record key to retrieve

Returns:

  • value of the record for that key, or nil if there is no record with that key

See Also:

  • #get(key)


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# File 'lib/lmdb/database.rb', line 29

def [](key)
  get(key)
end

#[]=(key, value) ⇒ Object

Set (write or update) a record in a database.

Examples:

db['a'] = 'b'     #=> 'b'
db['b'] = 1234    #=> 1234
db['a']           #=> 'b'

Parameters:

  • key —

    key for the record

  • value —

    the value of the record

Returns:

  • returns the value of the record

See Also:

  • value)


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# File 'lib/lmdb/database.rb', line 42

def []=(key, value)
  put key, value
  value
end

#cardinality(key) ⇒ Integer

Return the cardinality (number of duplicates) of a given key. Works whether :dupsort is set or not.

Parameters:

  • key (#to_s) —

    The key in question.

Returns:

  • (Integer) —

    The number of entries under the key.



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# File 'lib/lmdb/database.rb', line 100

def cardinality(key)
  ret = 0
  maybe_txn true do
  # env.transaction do
    if get key
      if dupsort?
        cursor do |c|
          c.set key
          ret = c.count
        end
      else
        ret = 1
      end
    end
  end
  ret
end

#clear ⇒ Object

Note:

The clear happens transactionally.

Empty out the database

Returns:

  • nil



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# File 'ext/lmdb_ext/lmdb_ext.c', line 1112

static VALUE database_clear(VALUE self) {
        DATABASE(self, database);
        if (!active_txn(database->env))
                return call_with_transaction(database->env, self, "clear", 0, 0, 0);
        check(mdb_drop(need_txn(database->env), database->dbi, 0));
        return Qnil;
}

#cursor {|cursor| ... } ⇒ Object

Create a cursor to iterate through a database. Uses current transaction, if any. Otherwise, if called with a block, creates a new transaction for the scope of the block. Otherwise, fails.

Examples:

db = env.database "abc"
db.cursor do |c|
  key, value = c.next
  puts "#{key}: #{value}"
end

Yields:

  • (cursor) —

    A block to be executed with the cursor.

Yield Parameters:

  • cursor (Cursor) —

    The cursor to be used to iterate

See Also:



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# File 'ext/lmdb_ext/lmdb_ext.c', line 1298

static VALUE database_cursor(VALUE self) {
        DATABASE(self, database);
        if (!active_txn(database->env)) {
                if (!rb_block_given_p()) {
                        rb_raise(cError, "Must call with block or active transaction.");
                }
                return call_with_transaction(database->env, self, "cursor", 0, 0, 0);
        }

        MDB_cursor* cur;
        check(mdb_cursor_open(need_txn(database->env), database->dbi, &cur));

        Cursor* cursor;
        VALUE vcur = Data_Make_Struct(cCursor, Cursor, cursor_mark, cursor_free, cursor);
        cursor->cur = cur;
        cursor->db = self;

        if (rb_block_given_p()) {
                int exception;
                VALUE ret = rb_protect(rb_yield, vcur, &exception);
                if (exception) {
                        cursor_close(vcur);
                        rb_jump_tag(exception);
                }
                cursor_close(vcur);
                return ret;
        }
        else {
                VALUE vtxn = environment_active_txn(database->env);
                if (NIL_P(vtxn)) {
                        rb_fatal("Internal error: transaction finished unexpectedly.");
                }
                else {
                        TRANSACTION(vtxn, txn);
                        rb_ary_push(txn->cursors, vcur);
                }
        }

        return vcur;
}

#delete(key, value = nil) ⇒ Object

Deletes records from the database. This function removes key/data pairs from the database. If the database does not support sorted duplicate data items (:dupsort) the value parameter is ignored. If the database supports sorted duplicates and the value parameter is nil, all of the duplicate data items for the key will be deleted. Otherwise, if the data parameter is non-nil only the matching data item will be deleted.

Parameters:

  • key —

    The key of the record to delete.

  • value —

    The optional value of the record to delete.

Raises:

  • (Error) —

    if the specified key/value pair is not in the database.



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# File 'ext/lmdb_ext/lmdb_ext.c', line 1225

static VALUE database_delete(int argc, VALUE *argv, VALUE self) {
        DATABASE(self, database);
        if (!active_txn(database->env))
                return call_with_transaction(database->env, self, "delete", argc, argv, 0);

        VALUE vkey, vval;
        rb_scan_args(argc, argv, "11", &vkey, &vval);

        vkey = StringValue(vkey);

        MDB_val key;
        key.mv_size = RSTRING_LEN(vkey);
        key.mv_data = RSTRING_PTR(vkey);

        if (NIL_P(vval)) {
                check(mdb_del(need_txn(database->env), database->dbi, &key, 0));
        } else {
                vval = StringValue(vval);
                MDB_val value;
                value.mv_size = RSTRING_LEN(vval);
                value.mv_data = RSTRING_PTR(vval);
                check(mdb_del(need_txn(database->env), database->dbi, &key, &value));
        }

        return Qnil;
}

#delete?(key, value = nil) ⇒ void

This method returns an undefined value.

Delete the key (and optional value pair) if it exists; do not complain about missing keys.

Parameters:

  • key (#to_s) —

    The key of the record

  • value (#to_s, nil) (defaults to: nil) —

    The optional value

See Also:



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# File 'lib/lmdb/database.rb', line 166

def delete?(key, value = nil)
  env.transaction { |txn| delete(key, value) if has?(key, value) }
end

#drop ⇒ Object

Note:

The drop happens transactionally.

Remove a database from the environment.

Returns:

  • nil



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# File 'ext/lmdb_ext/lmdb_ext.c', line 1098

static VALUE database_drop(VALUE self) {
        DATABASE(self, database);
        if (!active_txn(database->env))
                return call_with_transaction(database->env, self, "drop", 0, 0, 0);
        check(mdb_drop(need_txn(database->env), database->dbi, 1));
        return Qnil;
}

#dupfixed? ⇒ true, false

Returns whether the database is in :dupfixed mode.

Returns:

  • (true, false) 


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# File 'ext/lmdb_ext/lmdb_ext.c', line 1081

static VALUE database_is_dupfixed(VALUE self) {
        DATABASE(self, database);
        if (!active_txn(database->env))
                return call_with_transaction(database->env, self,
                                             "dupfixed?", 0, 0, MDB_RDONLY);
        unsigned int flags;
        check(mdb_dbi_flags(need_txn(database->env), database->dbi, &flags));

        return (flags & MDB_DUPFIXED) == 0 ? Qfalse : Qtrue;
}

#dupsort? ⇒ true, false

Returns whether the database is in :dupsort mode.

Returns:

  • (true, false) 


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# File 'ext/lmdb_ext/lmdb_ext.c', line 1065

static VALUE database_is_dupsort(VALUE self) {
        DATABASE(self, database);
        if (!active_txn(database->env))
                return call_with_transaction(database->env, self,
                                             "dupsort?", 0, 0, MDB_RDONLY);
        unsigned int flags;
        check(mdb_dbi_flags(need_txn(database->env), database->dbi, &flags));

        return (flags & MDB_DUPSORT) == 0 ? Qfalse : Qtrue;
}

#each {|i| ... } ⇒ Object

Iterate through the records in a database

Examples:

db.each do |record|
  key, value = record
  puts "at #{key}: #{value}"
end

Yields:

  • (i) —

    Gives a record [key, value] to the block

Yield Parameters:

  • i (Array) —

    The key, value pair for each record



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# File 'lib/lmdb/database.rb', line 13

def each
  maybe_txn true do
  # env.transaction do
    cursor do |c|
      while i = c.next
        yield(i)
      end
    end
  end
end

#each_key(&block) ⇒ Enumerator

Iterate over each key in the database, skipping over duplicate records.

Returns:

  • (Enumerator) —

    in lieu of a block.



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# File 'lib/lmdb/database.rb', line 57

def each_key(&block)
  return enum_for :each_key unless block_given?
  maybe_txn true do
  #env.transaction do
    cursor do |c|
      while (rec = c.next true)
        yield rec.first
      end
    end
  end
end

#each_value(key, &block) ⇒ Enumerator

Iterate over the duplicate values of a given key, using an implicit cursor. Works whether :dupsort is set or not.

Parameters:

  • key (#to_s) —

    The key in question.

Returns:

  • (Enumerator) —

    in lieu of a block.



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# File 'lib/lmdb/database.rb', line 75

def each_value(key, &block)
  return enum_for :each_value, key unless block_given?

  value = get(key) or return
  unless dupsort?
    yield value
    return
  end

  maybe_txn true do
  # env.transaction do
    cursor do |c|
      rec = c.set key
      while rec
        yield rec.last
        rec = c.next_range key
      end
    end
  end
end

#empty? ⇒ Boolean

Returns whether the database is empty.

Returns:

  • (Boolean) —

    whether the database is empty



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# File 'lib/lmdb/database.rb', line 179

def empty?
  stat[:entries] == 0
end

#env ⇒ Environment

Returns the environment to which this database belongs.

Returns:

  • (Environment) —

    the environment to which this database belongs.



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# File 'ext/lmdb_ext/lmdb_ext.c', line 1343

static VALUE database_env(VALUE self) {
        DATABASE(self, database);
        return database->env;
}

#flags ⇒ Hash

Return the flags used to open the database.

Returns:

  • (Hash) —

    The flags.



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# File 'ext/lmdb_ext/lmdb_ext.c', line 1048

static VALUE database_get_flags(VALUE self) {
        DATABASE(self, database);
        if (!active_txn(database->env))
                return call_with_transaction(database->env,
                                             self, "flags", 0, 0, MDB_RDONLY);
        unsigned int flags;
        check(mdb_dbi_flags(need_txn(database->env), database->dbi, &flags));
        return flags2hash(flags);
}

#get(key) ⇒ Object

Retrieves one value associated with this key. This function retrieves key/data pairs from the database. If the database supports duplicate keys (:dupsort) then the first data item for the key will be returned. Retrieval of other items requires the use of #cursor.

Parameters:

  • key —

    The key of the record to retrieve.



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# File 'ext/lmdb_ext/lmdb_ext.c', line 1129

static VALUE database_get(VALUE self, VALUE vkey) {
        DATABASE(self, database);
        if (!active_txn(database->env))
                return call_with_transaction(database->env, self, "get", 1, &vkey, MDB_RDONLY);

        vkey = StringValue(vkey);
        MDB_val key, value;
        key.mv_size = RSTRING_LEN(vkey);
        key.mv_data = RSTRING_PTR(vkey);

        int ret = mdb_get(need_txn(database->env), database->dbi, &key, &value);
        if (ret == MDB_NOTFOUND)
                return Qnil;
        check(ret);
        return rb_str_new(value.mv_data, value.mv_size);
}

#has?(key, value = nil) ⇒ Boolean

Test if the database has a given key (or, if opened in :dupsort, value)

Returns:

  • (Boolean) 


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# File 'lib/lmdb/database.rb', line 120

def has?(key, value = nil)
  v = get(key) or return false
  return true if value.nil? or value.to_s == v
  return false unless dupsort?

  # warn "checking dupsort value `#{value.inspect}` (#{value.class})"

  ret = false
  # read-only txn was having trouble being nested inside a read-write
  # maybe_txn(true) { cursor { |c| ret = !!c.set(key, value) } }
  env.transaction(true) { cursor { |c| ret = !!c.set(key, value) } }

  ret
end

#keys ⇒ Array

Get the keys as an array.

Returns:

  • (Array) —

    of keys.



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# File 'lib/lmdb/database.rb', line 49

def keys
  each_key.to_a
end

#put(key, value, options) ⇒ Object

Stores items into a database. This function stores key/value pairs in the database. The default behavior is to enter the new key/value pair, replacing any previously existing key if duplicates are disallowed, or adding a duplicate data item if duplicates are allowed (:dupsort).

Parameters:

  • key —

    The key of the record to set

  • value —

    The value to insert for this key

Options Hash (options):

  • :nodupdata (Boolean) —

    Enter the new key/value pair only if it does not already appear in the database. This flag may only be specified if the database was opened with :dupsort. The function will raise an Error if the key/data pair already appears in the database.

  • :nooverwrite (Boolean) —

    Enter the new key/value pair only if the key does not already appear in the database. The function will raise an {Error] if the key already appears in the database, even if the database supports duplicates (:dupsort).

  • :append (Boolean) —

    Append the given key/data pair to the end of the database. No key comparisons are performed. This option allows fast bulk loading when keys are already known to be in the correct order. Loading unsorted keys with this flag will cause data corruption.

  • :appenddup (Boolean) —

    As above, but for sorted dup data.



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# File 'ext/lmdb_ext/lmdb_ext.c', line 1179

static VALUE database_put(int argc, VALUE *argv, VALUE self) {
    DATABASE(self, database);
    if (!active_txn(database->env))
        return call_with_transaction(database->env, self, "put", argc, argv, 0);

    VALUE vkey, vval, option_hash = Qnil;
#ifdef RB_SCAN_ARGS_KEYWORDS
    rb_scan_args_kw(RB_SCAN_ARGS_LAST_HASH_KEYWORDS,
                    argc, argv, "20:", &vkey, &vval, &option_hash);
#else
    rb_scan_args(argc, argv, "20:", &vkey, &vval, &option_hash);
#endif

    int flags = 0;
    if (!NIL_P(option_hash))
        rb_hash_foreach(option_hash, (int (*)(ANYARGS))database_put_flags,
                        (VALUE)&flags);

    vkey = StringValue(vkey);
    vval = StringValue(vval);

    MDB_val key, value;
    key.mv_size = RSTRING_LEN(vkey);
    key.mv_data = RSTRING_PTR(vkey);
    value.mv_size = RSTRING_LEN(vval);
    value.mv_data = RSTRING_PTR(vval);

    check(mdb_put(need_txn(database->env), database->dbi, &key, &value, flags));
    return Qnil;
}

#put?(key, value = nil, **options) ⇒ void

This method returns an undefined value.

Conditionally put a value into the database.

Parameters:

  • key (#to_s) —

    The key of the record

  • value (#to_s, nil) (defaults to: nil) —

    the (optional) value

  • options (Hash) —

    options

See Also:



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# File 'lib/lmdb/database.rb', line 145

def put?(key, value = nil, **options)
  # early bailout
  return if value.nil?

  flags = { (dupsort? ? :nodupdata : :nooverwrite) => true }

  env.transaction do |txn|
    put(key, value, **options.merge(flags)) unless has?(key, value)
  end
end

#size ⇒ Object

Return how many records there are in this database.

Returns:

  • the number of records in this database



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# File 'lib/lmdb/database.rb', line 173

def size
  stat[:entries]
end

#stat ⇒ Hash

Return useful statistics about a database.

  • :psize Size of a database page

  • :depth Depth (height) of the B-tree

  • :branch_pages Number of internal (non-leaf) pages

  • :leaf_pages Number of leaf pages

  • :overflow_pages Number of overflow pages

  • :entries Number of data items

Returns:

  • (Hash) —

    the statistics



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# File 'ext/lmdb_ext/lmdb_ext.c', line 1032

static VALUE database_stat(VALUE self) {
        DATABASE(self, database);
        if (!active_txn(database->env))
                return call_with_transaction(database->env,
                                             self, "stat", 0, 0, MDB_RDONLY);

        MDB_stat stat;
        check(mdb_stat(need_txn(database->env), database->dbi, &stat));
        return stat2hash(&stat);
}