Get<A> abstract mixin

abstract mixin class Get<A>

Describes how to read a value of type A from a single column position in a database result Row.

Constructors

Get()

Get()

Properties

hashCode no setter inherited

int get hashCode

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

Inherited from Object.

Implementation

external int get hashCode;

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

Methods

emap()

Get<B> emap<B>(Either<String, B> Function(A) f)

Transforms the decoded value with f, which may fail with an error message (left) or succeed with a new value (right).

Implementation

Get<B> emap<B>(Function1<A, Either<String, B>> f) => _EmapGet(this, f);

map()

Get<B> map<B>(B Function(A) f)

Transforms the decoded value by applying f.

Implementation

Get<B> map<B>(Function1<A, B> f) => _MapGet(this, f);

noSuchMethod() inherited

dynamic noSuchMethod(Invocation invocation)

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

Implementation

@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

toString() inherited

String toString()

A string representation of this object.

Some classes have a default textual representation, often paired with a static parse function (like int.parse). These classes will provide the textual representation as their string representation.

Other classes have no meaningful textual representation that a program will care about. Such classes will typically override toString to provide useful information when inspecting the object, mainly for debugging or logging.

Inherited from Object.

Implementation

external String toString();

unsafeGet()

A unsafeGet(Row row, int n)

Extracts a value of type A from row at column index n.

This is considered "unsafe" because it may throw if the column is missing or contains an incompatible type.

Implementation

A unsafeGet(Row row, int n);

Operators

operator ==() inherited

bool operator ==(Object other)

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

• Total: It must return a boolean for all arguments. It should never throw.

• Reflexive: For all objects o, o == o must be true.

• Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

• Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

If a subclass overrides the equality operator, it should override the hashCode method as well to maintain consistency.

Inherited from Object.

Implementation

external bool operator ==(Object other);

Static Properties

bigInt final

final Get<BigInt> bigInt

Reads a BigInt from a single column.

Implementation

static final Get<BigInt> bigInt = _genericGet();

blob final

final Get<ByteVector> blob

Reads a binary blob from a single column.

Implementation

static final Get<ByteVector> blob = _genericGet<List<int>>().map(ByteVector.fromDart);

boolean final

final Get<bool> boolean

Reads a boolean from a single column (stored as 0/1 integer).

Implementation

static final Get<bool> boolean = integer.map((i) => i != 0);

dateTime final

final Get<DateTime> dateTime

Reads a DateTime from a single column (stored as an ISO 8601 string).

Implementation

static final Get<DateTime> dateTime = string.emap(
  (str) => Either.catching(
    () => DateTime.parse(str),
    (err, _) => err.toString(),
  ),
);

dubble final

final Get<double> dubble

Reads a double from a single column.

Implementation

static final Get<double> dubble = _genericGet();

integer final

final Get<int> integer

Reads an int from a single column.

Implementation

static final Get<int> integer = _genericGet();

json final

final Get<Json> json

Reads a Json value from a single column (stored as a JSON string).

Implementation

static final Get<Json> json = string.emap(
  (str) => Json.parse(str).leftMap((failure) => failure.message),
);

string final

final Get<String> string

Reads a String from a single column.

Implementation

static final Get<String> string = _genericGet();

Static Methods

instance()

Get<A> instance<A>(A Function(Row, int) f)

Creates a Get from a function that extracts a value from a Row at column index n.

Implementation

static Get<A> instance<A>(Function2<Row, int, A> f) => _GetF(f);