Module serde_db::de

Support for deserializing database resultsets, and/or individual database rows, and/or individual database values, into rust types.

Result sets

Rather than iterating over rows and columns of a resultset, applications can convert resultsets directly into their data structure of choice.

This approach allows, in contrast to many ORM mapping variants, using the full flexibility of SQL (projection lists, all kinds of joins, unions, etc, etc). Whatever query an application needs, they just use it, and whatever result structure they need, they just use a corresponding rust structure or tuple into which they deserialize the data in a single method call.

The target types for deserialization only need to implement serde::de::Deserialize, which is automatically given for all elementary rust types and tuples, and easily achieved for custom structs using #[derive(Deserialize)].

Result sets can always be deserialized into a Vec<line_struct>, where line_struct matches the field list of the resultset and implements serde::de::Deserialize.

Similarly, a Vec<(...)>, works as well, as long as the tuple members match the field list of the resultset.

In addition, serde_db also supports structural simplification: depending on the dimension of the resultset, simplified target types can be chosen for deserialization:

• If the resultset contains only a single line (e.g. because you specified TOP 1 in your select), then you can optionally choose to deserialize directly into a plain line_struct.

• If the resultset contains only a single column, then you can optionally choose to deserialize into a Vec<plain_field>.

• If the resultset contains only a single value (one row with one column), then you can optionally choose to deserialize into a plain line_struct, or a Vec<plain_field>, or a plain variable.

The below examples assume the DB driver exposes on its resultset type a function fn into_typed<'de, T: serde::de::Deserialize<'de>>(self) -> mock_db::Result<T>, which is implemented using serde_db.

Convert a n×m resultset into a Vec of structs:

#[derive(serde_derive::Deserialize)]
struct MyStruct {
  // ...
}

// let resultset = ...;
let data: Vec<MyStruct> = resultset.into_typed()?;

Note that MyStruct has to implement serde::de::Deserialize.

Convert a n×1 resultset into a Vec of fields:

let vec_s: Vec<String> = resultset.into_typed()?;

Convert a 1×1 resultset into a single field:

let s: String = resultset.into_typed()?;

Rows

Convert rows into tuples or structs

For better streaming of large resultsets, you might want to iterate over the rows, like in

for row in resultset {
    let t: (String, NaiveDateTime, i32, Option<i32>) = row.into_typed()?;
}

or

for row in resultset {
    let data: MyStruct = row.into_typed()?;
}

Individual values

When necessary, you can also convert individual values directly into an adequate rust type:

for row in resultset {
    let date: NaiveDateTime = row.field_into_typed(2)?;
    ...
}

Note for implementors

Implementing DB drivers need to implement DeserializableResultset and DeserializableRow, which are trivial, and DbValue, which is a bit more effort (an example can be found in the tests of this crate), depending on the flexibility you want to offer.

We further recommend adding a method like into_typed() directly on the driver's class for resultsets with a plain delegation to the provided method DeserializableResultset::into_typed(). The same should be done for rows.

By this, the deserialization functionality of serde_db can be provided to the users of the DB driver without forcing them to import serde_db.

Enums

ConversionError	An error type for implementors of DbValue.
DeserializationError	The errors that can arise while deserializing with serde_db::de.

Traits

DbValue	Provides the conversion of a database value into a standard rust type.
DbValueInto	Converts the given database value into a specific rust type.
DeserializableResultset	Interface for a database resultset to support deserialization.
DeserializableRow	A minimal interface for the Row type to support the deserialization.

Type Definitions

DeserializationResult

A specialized Result type for deserialization.