[Hiki] update - tut-libgda-datamodels (ruby-gnome2-doc-cvs) - Ruby-GNOME2

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- = Managing data models
+ = Managing data models and values

  Each time we execute a normal query, we will obtain a Gda::DataModel object, which is the way to see what the query returned.

  Before continuing, we must say that it is possible to modify a data model, but as we are accessing using SQL, it is not recommended to modify it, so modifications on the database must be done using SQL.
+ 
+ A data model contains a set of rows (Gda::Row), according to the query.  Rows contain a set of values (Gda::Value) for each column of the data model.  Values embed various kind of data (strings, integers, booleans, dates, money currencies, etc...).
+ 
+ You can use Gda::Value#to_s to retrieve a string representation of a GDA value, and you can compare values using Gda::Value#<=>. 
+ 
+ [TODO: introduce Gda::Value#to_* conversion methods]

  == Example using direct cell access

  This method accesses the data model by directly accessing cells, using Gda::DataModel#get_value_at:

    def show_table(dm)
        # Loop for writing column names.
        dm.n_columns.times { |n_col| puts dm.get_column_title(n_col) }
        puts ""
        # Double loop accessing values using Gda::DataModel#get_value_at.
        dm.n_columns.times do |n_col|
            dm.n_rows.times do |n_row|
                # Data returned is a Gda::Value object.
                val = dm.get_value_at(n_col, n_row)
                puts val.to_s
            end
        end
    end

  == Example using row access

  This method accesses the data model by accessing rows, using Gda::DataModel#get_row and Gda::DataModel#get_value:

    def show_table2(dm)
        # Loop for writing column names.
        dm.n_columns.times { |n_col| puts dm.get_column_title(n_col) }
        puts ""
        # Outer loop obtaining rows using Gda::DataModel#get_row.
        dm.n_rows.times do |n_row|
            row = dm.get_row(n_row)
            # Inner loop obtaining the value using Gda::DataModel#get_value.
            dm.n_columns.times do |n_col|
                val = row.get_value(n_col)
                puts val.to_s
            end
        end
    end

  == Example using 'The Ruby Way'

  For your convenience, Ruby/Libgda provides a more rubish way to access values in data models.

  Just have a look at the following methods: Gda::DataModel#each_column, Gda::DataModel#columns, Gda::DataModel#each_row, Gda::DataModel#rows, Gda::Row#each_value and Gda::Row#values.

  Here is an example using iterators:

    def show_table3(dm)
        dm.each_column { |title| puts title }
        puts ""
        dm.each_row { |row| row.each_value { |val| puts val.to_s } }
    end

  Life is good, isn't it? ;-)

Ruby-GNOME2

[ruby-gnome2-doc-cvs] [Hiki] update - tut-libgda-datamodels