Struct hdbconnect::types::NCLob

pub struct NCLob(_);

LOB implementation for unicode Strings that is used with HdbValue::NCLOB instances coming from the database.

Bigger LOBs are not transferred completely in the first roundtrip, instead more data are fetched in subsequent roundtrips when they are 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 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 max_buf_len(&self) -> usize

Returns the maximum size the internal buffers ever had, in bytes.

This method exists mainly for debugging purposes. With streaming, the returned value is not supposed to exceed 3 times lob_read_length (see Connection::set_lob_read_length) plus the buffer size used by the reader.

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

pub fn clone(&self) -> NCLob

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for NCLob

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

Formats the value using the given formatter.

impl Read for NCLob

pub 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.

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

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

pub 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.

pub unsafe fn initializer(&self) -> Initializer

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

Determines if this Reader can work with buffers of uninitialized memory.

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

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

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

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

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

Read the exact number of bytes required to fill buf.

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

Creates a "by reference" adaptor for this instance of Read.

pub fn bytes(self) -> Bytes<Self>

Transforms this Read instance to an Iterator over its bytes.

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

Creates an adaptor which will chain this stream with another.

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

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