F3.
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Stitches physical columns into logical fields.
The footer leaves nested physical columns unnamed. This module walks the schema in the same order as the pinned reader: a struct consumes a boolean validity column and then its children, and a list consumes an offset column and then its child. The logical tree must describe that same shape. A disagreement stops the read.
Summary
Functions
Builds logical columns for names from physical columns keyed by index.
The logical tree and the Arrow schema describe the same nesting.
Physical {index, type} pairs required by the named top-level fields.
Functions
@spec assemble([F3.Schema.field()], [String.t()], %{ required(non_neg_integer()) => F3.Column.t() }) :: {:ok, %{optional(String.t()) => F3.Column.t()}} | {:error, F3.Error.t()}
Builds logical columns for names from physical columns keyed by index.
physical maps a physical index to an F3.Column. A missing column is
an error. The result maps each requested name to its logical column.
Examples
iex> field = %{name: "id", type: {:int, 64, true}, nullable: false}
iex> {:ok, physical} = F3.Column.from_native(:i64, 1, <<5::little-64>>, nil)
iex> {:ok, %{"id" => column}} = F3.Logical.assemble([field], ["id"], %{0 => physical})
iex> F3.Column.value(column, 0)
5@spec matches?(F3.Metadata.logical_tree() | nil, [F3.Schema.field()]) :: boolean()
The logical tree and the Arrow schema describe the same nesting.
The tree must be %{id: :struct, children: nodes} with one child per
field. A flat child matches a primitive field. Any other shape is false.
This does not raise.
Examples
iex> field = %{name: "id", type: {:int, 64, true}, nullable: false}
iex> tree = %{id: :struct, children: [%{id: :flat, children: []}]}
iex> F3.Logical.matches?(tree, [field])
true
iex> F3.Logical.matches?(nil, [field])
false@spec needed([F3.Schema.field()], [String.t()]) :: {:ok, [{non_neg_integer(), atom()}]} | {:error, F3.Error.t()}
Physical {index, type} pairs required by the named top-level fields.
fields is the schema. names selects top-level fields. A name that is
not present contributes no pairs. An unclaimed primitive is
:unsupported_encoding.
Examples
iex> field = %{name: "id", type: {:int, 64, true}, nullable: false}
iex> F3.Logical.needed([field], ["id"])
{:ok, [{0, :i64}]}
iex> F3.Logical.needed([field], ["other"])
{:ok, []}