How deeply does Learn Haskell by Example cover FromRow?

Defines RowParser construction with FromField and field, then demonstrates explicit and generic instances without detailing custom parser internals.

FromRow

As explained in Learn Haskell by Example

FromRow is a sqlite-simple type class whose instances define parsing of SQL row data into Haskell values.

FromRow is a sqlite-simple type class for reading SQL query results as Haskell values. Its fromRow method defines a RowParser that converts database row data into a chosen result type. section 16.3.2

Each column is parsed with FromField through field. Applicative syntax combines those field parsers in column order, matching a constructor’s arguments. section 16.3.2

Parsing a TodoEntry

A TodoEntry instance can read four selected columns directly: fromRow = TodoEntry <$> field <*> field <*> field <*> field. Registering this instance lets query_ return [TodoEntry], while SQLite integer values are converted into the corresponding Haskell fields.

For standard data types, sqlite-simple supplies FromField parsers. Generic can also derive FromRow and ToRow instances when the datatype definition provides the required structure. section 16.4

How Learn Haskell by Example covers it

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Also explained in

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Rust Servers, Services, and AppsFromRow is an SQLx trait for constructing a Rust value from a database query result row.

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Related concepts

SQLused by · SQL is a standardized declarative language for defining, querying, and manipulating data and structures in relational database systems.
query_as! macroproduced by · query_as! is an SQLx compile-time macro that maps SQL query results into a specified Rust type and checks the query against the database schema.
SQLxused by · SQLx is a Rust asynchronous toolkit for interacting with relational databases, mapping query results to Rust types, and optionally checking SQL queries at compile time.
ToRowcontrasts with · ToRow is a sqlite-simple type class for converting Haskell values into parameters that can be bound to SQL statements.

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