Module odbc_api::buffers

Using buffers to fetch results

The most efficient way to query results is not query an ODBC data source row by row, but to ask for a whole bulk of rows at once. The ODBC driver and driver manager will then fill these row sets into buffers which have been previously bound. This is also the most efficient way to query a single row many times for many queries, if the application can reuse the bound buffer. This crate allows you to provide your own buffers by implementing the crate::RowSetBuffer trait. That however requires unsafe code.

This crate also provides three implementations of the crate::RowSetBuffer trait, ready to be used in safe code:

• crate::buffers::ColumnarBuffer: Binds to the result set column wise. This is usually helpful in dataengineering or data sciense tasks. This buffer type can be used in situations there the schema of the queried data is known at compile time, as well as for generic applications which do work with wide range of different data. Checkt the struct documentation for examples.
• crate::buffers::TextRowSet: Queries all data as text bound in columns. Since the columns are homogeneous, you can also use this, to iterate row wise over the buffer. Excellent if you want to print the contents of a table, or are for any reason only interessted in the text representation of the values.
• crate::buffers::RowVec: A good choice if you know the schema at compile time and your application logic is build in a row by row fashion, rather than column by column.

Structs

• BinColumn
  A buffer intended to be bound to a column of a cursor. Elements of the buffer will contain a variable amount of bytes up to a maximum length. Since elements of this type have variable length an additional indicator buffer is also maintained, whether the column is nullable or not. Therefore this buffer type is used for variable sized binary data whether it is nullable or not.
• BinColumnIt
  Iterator over a binary column. See crate::buffers::BinColumn
• BinColumnSliceMut
  A view to a mutable array parameter text buffer, which allows for filling the buffer with values.
• BinColumnView
• ColumnarBuffer
  A columnar buffer intended to be bound with crate::Cursor::bind_buffer in order to obtain results from a cursor.
• NullableSlice
  Iterates over the elements of a column buffer. Returned by crate::buffers::ColumnarBuffer::column as part of an crate::buffers::AnySlice.
• NullableSliceMut
  Used to fill a column buffer with an iterator. Returned by crate::ColumnarBulkInserter::column_mut as part of an crate::buffers::AnySliceMut.
• RowVec
  A row wise buffer intended to be bound with crate::Cursor::bind_buffer in order to obtain results from a cursor.
• TextColumn
  A buffer intended to be bound to a column of a cursor. Elements of the buffer will contain a variable amount of characters up to a maximum string length. Since most SQL types have a string representation this buffer can be bound to a column of almost any type, ODBC driver and driver manager should take care of the conversion. Since elements of this type have variable length an indicator buffer needs to be bound, whether the column is nullable or not, and therefore does not matter for this buffer.
• TextColumnIt
  Iterator over a text column. See TextColumnView::iter
• TextColumnSliceMut
  A view to a mutable array parameter text buffer, which allows for filling the buffer with values.
• TextColumnView
  Allows read only access to the valid part of a text column.

Enums

• AnyBuffer
  Buffer holding a single column of either a result set or paramater
• AnySlice
  A borrowed view on the valid rows in a column of a crate::buffers::ColumnarBuffer.
• AnySliceMut
  A mutable slice of an input buffer, with runtime type information. Edit values in this slice in order to send parameters in bulk to a database.
• BufferDesc
  Describes a column of a crate::buffers::ColumnarBuffer.
• Indicator
  Indicates existence and length of a value.

Traits

• ColumnBuffer
  A buffer for a single column intended to be used together with ColumnarBuffer.
• FetchRow
  FetchRows can be bound to a crate::Cursor to enable row wise (bulk) fetching of data as opposed to column wise fetching. Since all rows are bound to a C-API in a contigious block of memory the row itself should be representable as such. Concretly that means that types like String can not be supported directly by FetchRows for efficient bulk fetching, due to the fact it points to data on the heap.
• FetchRowMember
  Can be used as a member of a FetchRow and bound to a column during row wise fetching.
• Item
  Can either be extracted as a slice or a NullableSlice from an AnySlice. This allows the user to avoid matching on all possibile variants of an AnySlice in case the buffered type is known at compile time.

Type Aliases

• CharColumn
  A column buffer for character data. The actual encoding used may depend on your system locale.
• ColumnarAnyBuffer
  Flexible columnar buffer implementation. Bind this to a cursor to fetch values in bulk, or pass this as a parameter to a statement, to submit many parameters at once.
• TextRowSet
  This row set binds a string buffer to each column, which is large enough to hold the maximum length string representation for each element in the row set at once.
• WCharColumn
  This buffer uses wide characters which implies UTF-16 encoding. UTF-8 encoding is preferable for most applications, but contrary to its sibling crate::buffers::CharColumn this buffer types implied encoding does not depend on the system locale.