Struct hdbconnect_impl::sync::NCLob

pub struct NCLob(/* private fields */);

LOB implementation for unicode Strings.

NCLob is used within HdbValue::NCLOB instances received from the database.

Bigger LOBs are not transferred completely in the first roundtrip, instead more data is fetched in subsequent roundtrips when needed.

NCLob respects the Connection’s lob read length (see Connection::set_lob_read_length) by transferring per fetch request lob_read_length unicode characters (rather than bytes). Note that due to the way how HANA represents unicode internally, all BMP-0 characters count as 1, non-BMP-0 characters count as 2.

Implementations

impl NCLob

pub fn into_string(self) -> HdbResult<String>

Converts the NCLob into the contained String.

All outstanding data (data that were not yet fetched from the server) are fetched into this NCLob object, before the complete data, as far as they were not yet read from this NCLob object, are returned.

Example

 let mut resultset = connection.query(query)?;
 let mut nclob = resultset.into_single_row()?.into_single_value()?.try_into_nclob()?;
 let s = nclob.into_string(); // String, can be huge

Alternative

For larger objects, a streaming approach using the Read implementation of NCLob might by more appropriate, to avoid total allocation of the large object.

Example

 let mut writer;
 // ... writer gets instantiated, is an implementation of std::io::Write;

 std::io::copy(&mut nclob, &mut writer)?;

Errors

Several variants of HdbError can occur.

pub fn write_into(self, writer: &mut dyn Write) -> HdbResult<()>

Writes the content into the given writer.

Reads outstanding data in chunks of size Connection::lob_read_length from the database and writes them immediately into the writer, thus avoiding that all data are materialized within this NCLob.

pub fn read_slice( &mut self, offset: u64, length: u32 ) -> HdbResult<CharLobSlice>

Reads from given offset and the given length, in number of unicode characters.

Note that due to the way how HANA represents unicode internally, all BMP-0 characters count as 1, non-BMP-0 characters count as 2.

Errors

Several variants of HdbError can occur.

pub fn total_byte_length(&self) -> u64

Total length of data, in bytes.

pub fn total_char_length(&self) -> u64

Total length of data, in characters.

Note that due to the way how HANA represents unicode internally, all BMP-0 characters count as 1, non-BMP-0 characters count as 2.

pub fn is_empty(&self) -> bool

Returns true if the NCLob does not contain data.

pub fn cur_buf_len(&self) -> usize

Current size of the internal buffer, in bytes.

pub fn server_usage(&self) -> ServerUsage

Provides information about the the server-side resource consumption that is related to this NCBLob object.

Trait Implementations

impl Clone for NCLob

fn clone(&self) -> NCLob

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for NCLob

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Read for NCLob

fn read(&mut self, buf: &mut [u8]) -> Result<usize>

Pull some bytes from this source into the specified buffer, returning how many bytes were read.

fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize, Error>

Like read, except that it reads into a slice of buffers.

fn is_read_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector)

Determines if this Reader has an efficient read_vectored implementation.

fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize, Error>

Read all bytes until EOF in this source, placing them into buf.

fn read_to_string(&mut self, buf: &mut String) -> Result<usize, Error>

Read all bytes until EOF in this source, appending them to buf.

fn read_exact(&mut self, buf: &mut [u8]) -> Result<(), Error>

Read the exact number of bytes required to fill buf.

fn read_buf(&mut self, buf: BorrowedCursor<'_>) -> Result<(), Error>

🔬This is a nightly-only experimental API. (read_buf)

Pull some bytes from this source into the specified buffer.

fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<(), Error>

🔬This is a nightly-only experimental API. (read_buf)

Read the exact number of bytes required to fill cursor.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adaptor for this instance of Read.

fn bytes(self) -> Bytes<Self>

where Self: Sized,

Transforms this Read instance to an Iterator over its bytes.

fn chain<R>(self, next: R) -> Chain<Self, R>

where R: Read, Self: Sized,

Creates an adapter which will chain this stream with another.

fn take(self, limit: u64) -> Take<Self>

where Self: Sized,

Creates an adapter which will read at most limit bytes from it.