Struct PostgresRdbcItemReader 

pub struct PostgresRdbcItemReader<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

Prefer RdbcItemReaderBuilder for ergonomic construction.

Implementations

impl<I> PostgresRdbcItemReader<I>

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

pub fn new( pool: Pool<Postgres>, query: String, 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.

Prefer RdbcItemReaderBuilder for a more ergonomic construction API.

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.
• keyset_column - Optional column name for keyset pagination.
• keyset_key - Optional closure to extract the cursor value from an item.

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.

Manages automatic pagination: loads a new page when the buffer is exhausted, handles both LIMIT/OFFSET and keyset pagination transparently.

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;
use spring_batch_rs::item::rdbc::RdbcItemReaderBuilder;
use sqlx::PgPool;

let pool = PgPool::connect("postgresql://user:pass@localhost/db").await?;
let reader = RdbcItemReaderBuilder::<User>::new()
    .postgres(pool)
    .query("SELECT id, name FROM users ORDER BY id")
    .with_page_size(100)
    .build_postgres();

// 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);