Struct PostgresRdbcItemReader 

pub struct PostgresRdbcItemReader<'a, I>
where
    for<'r> I: FromRow<'r, PgRow> + Send + Unpin + Clone,
{ /* private fields */ }

Available on crate feature rdbc only.

PostgreSQL RDBC Item Reader for batch processing.

Supports two pagination strategies:

• LIMIT/OFFSET (default): simple but degrades at large offsets — use for small datasets.
• Keyset pagination (recommended for large datasets): uses WHERE col > :last ORDER BY col LIMIT n, O(log n) per page regardless of dataset size. Enable with [RdbcItemReaderBuilder::with_keyset].

Type Parameters

• I - Must implement FromRow<PgRow> + Send + Unpin + Clone.

Construction

Use [RdbcItemReaderBuilder] — direct construction is not available.

Implementations

impl<'a, I> PostgresRdbcItemReader<'a, I>

where for<'r> I: FromRow<'r, PgRow> + Send + Unpin + Clone,

pub fn new( pool: Pool<Postgres>, query: &'a str, page_size: Option<i32>, keyset_column: Option<String>, keyset_key: Option<Box<dyn Fn(&I) -> String>>, ) -> Self

Creates a new PostgresRdbcItemReader with the specified parameters

This constructor is only accessible within the crate to enforce the use of RdbcItemReaderBuilder for creating reader instances.

Arguments

• pool - PostgreSQL connection pool for database operations
• query - SQL query to execute (without LIMIT/OFFSET)
• page_size - Optional page size for pagination. None means read all at once.

Returns

A new PostgresRdbcItemReader instance ready for use.

Trait Implementations

impl<I> ItemReader<I> for PostgresRdbcItemReader<'_, I>

where for<'r> I: FromRow<'r, PgRow> + Send + Unpin + Clone,

fn read(&self) -> ItemReaderResult<I>

Reads the next item from the PostgreSQL database

This method implements the ItemReader trait and provides the core reading logic with automatic pagination management:

1. Index Calculation: Determines the current position within the current page
2. Page Loading: Loads a new page if we’re at the beginning of a page
3. Item Retrieval: Returns the item at the current position from the buffer
4. Offset Management: Advances the offset for the next read operation

Pagination Logic

For paginated reading (when page_size is Some):

• index = offset % page_size gives position within current page
• When index == 0, we’re at the start of a new page and need to load data
• Buffer contains only the current page’s items

For non-paginated reading (when page_size is None):

• index = offset gives absolute position in the full result set
• Data is loaded only once when index == 0 (first read)
• Buffer contains all items from the query

Returns

• Ok(Some(item)) if an item was successfully read
• Ok(None) if there are no more items to read (end of result set)
• Err(BatchError::ItemReader) if a database error occurred

Examples

use spring_batch_rs::core::item::ItemReader;

let reader = PostgresRdbcItemReader::<User>::new(
    pool,
    "SELECT id, name FROM users ORDER BY id",
    Some(100)
);

// Read items one by one
let mut count = 0;
while let Some(user) = reader.read()? {
    println!("User: {} - {}", user.id, user.name);
    count += 1;
}
println!("Processed {} users", count);