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# QSqlField Class Reference
[QtSql module]

The QSqlField class manipulates the fields in SQL database tables and views. More...

### Types

- enum RequiredStatus { Unknown, Optional, Required }

### Methods

- __init__ (self, QString fieldName = QString(), QVariant.Type type = QVariant.Invalid)
- __init__ (self, QSqlField)
- clear (self)
- QVariant defaultValue (self)
- bool isAutoValue (self)
- bool isGenerated (self)
- bool isNull (self)
- bool isReadOnly (self)
- bool isValid (self)
- int length (self)
- QString name (self)
- int precision (self)
- RequiredStatus requiredStatus (self)
- setAutoValue (self, bool)
- setDefaultValue (self, QVariant)
- setGenerated (self, bool)
- setLength (self, int)
- setName (self, QString)
- setPrecision (self, int)
- setReadOnly (self, bool)
- setRequired (self, bool)
- setRequiredStatus (self, RequiredStatus)
- setSqlType (self, int)
- setType (self, QVariant.Type)
- setValue (self, QVariant)
- QVariant.Type type (self)
- int typeID (self)
- QVariant value (self)

### Special Methods

- bool __eq__ (self, QSqlField)
- bool __ne__ (self, QSqlField)

## Detailed Description

The QSqlField class manipulates the fields in SQL database tables and views.

QSqlField represents the characteristics of a single column in a database table or view, such as the data type and column name. A field also contains the value of the database column, which can be viewed or changed.

Field data values are stored as QVariants. Using an incompatible type is not permitted. For example:

         QSqlField field("age", QVariant.Int);
         field.setValue(QPixmap());  // WRONG

However, the field will attempt to cast certain data types to the field data type where possible:

         QSqlField field("age", QVariant.Int);
         field.setValue(QString("123"));  // casts QString to int

QSqlField objects are rarely created explicitly in application code. They are usually accessed indirectly through QSqlRecords that already contain a list of fields. For example:

         QSqlQuery query;
         ...
         QSqlRecord record = query.record();
         QSqlField field = record.field("country");

A QSqlField object can provide some meta-data about the field, for example, its name(), variant type(), length(), precision(), defaultValue(), typeID(), and its requiredStatus(), isGenerated() and isReadOnly(). The field's data can be checked to see if it isNull(), and its value() retrieved. When editing the data can be set with setValue() or set to NULL with clear().

See also QSqlRecord.

## Type Documentation

### QSqlField.RequiredStatus

Specifies whether the field is required or optional.

Constant | Value | Description
--- | --- | ---
`QSqlField.Required` | `1` | The field must be specified when inserting records.
`QSqlField.Optional` | `0` | The fields doesn't have to be specified when inserting records.
`QSqlField.Unknown` | `-1` | The database driver couldn't determine whether the field is required or optional.

See also requiredStatus().

## Method Documentation

### QSqlField.__init__ (self, QString fieldName = QString(), QVariant.Type type = QVariant.Invalid)

Constructs an empty field called fieldName of variant type type.

See also setRequiredStatus(), setLength(), setPrecision(), setDefaultValue(), setGenerated(), and setReadOnly().

### QSqlField.__init__ (self, QSqlField)

Constructs a copy of other.

### QSqlField.clear (self)

Clears the value of the field and sets it to NULL. If the field is read-only, nothing happens.

See also setValue(), isReadOnly(), and requiredStatus().

### QVariant QSqlField.defaultValue (self)

Returns the field's default value (which may be NULL).

See also setDefaultValue(), type(), requiredStatus(), length(), precision(), and isGenerated().

### bool QSqlField.isAutoValue (self)

Returns true if the value is auto-generated by the database, for example auto-increment primary key values.

See also setAutoValue().

### bool QSqlField.isGenerated (self)

Returns true if the field is generated; otherwise returns false.

See also setGenerated(), type(), requiredStatus(), length(), precision(), and defaultValue().

### bool QSqlField.isNull (self)

Returns true if the field's value is NULL; otherwise returns false.

See also value().

### bool QSqlField.isReadOnly (self)

Returns true if the field's value is read-only; otherwise returns false.

See also setReadOnly(), type(), requiredStatus(), length(), precision(), defaultValue(), and isGenerated().

### bool QSqlField.isValid (self)

Returns true if the field's variant type is valid; otherwise returns false.

### int QSqlField.length (self)

Returns the field's length.

If the returned value is negative, it means that the information is not available from the database.

See also setLength(), type(), requiredStatus(), precision(), defaultValue(), and isGenerated().

### QString QSqlField.name (self)

Returns the name of the field.

See also setName().

### int QSqlField.precision (self)

Returns the field's precision; this is only meaningful for numeric types.

If the returned value is negative, it means that the information is not available from the database.

See also setPrecision(), type(), requiredStatus(), length(), defaultValue(), and isGenerated().

### RequiredStatus QSqlField.requiredStatus (self)

Returns true if this is a required field; otherwise returns false. An `INSERT` will fail if a required field does not have a value.

See also setRequiredStatus(), type(), length(), precision(), defaultValue(), and isGenerated().

### QSqlField.setAutoValue (self, bool)

Marks the field as an auto-generated value if autoVal is true.

See also isAutoValue().

### QSqlField.setDefaultValue (self, QVariant)

Sets the default value used for this field to value.

See also defaultValue(), value(), setType(), setRequiredStatus(), setLength(), setPrecision(), setGenerated(), and setReadOnly().

### QSqlField.setGenerated (self, bool)

Sets the generated state. If gen is false, no SQL will be generated for this field; otherwise, Qt classes such as QSqlQueryModel and QSqlTableModel will generate SQL for this field.

See also isGenerated(), setType(), setRequiredStatus(), setLength(), setPrecision(), setDefaultValue(), and setReadOnly().

### QSqlField.setLength (self, int)

Sets the field's length to fieldLength. For strings this is the maximum number of characters the string can hold; the meaning varies for other types.

See also length(), setType(), setRequiredStatus(), setPrecision(), setDefaultValue(), setGenerated(), and setReadOnly().

### QSqlField.setName (self, QString)

Sets the name of the field to name.

See also name().

### QSqlField.setPrecision (self, int)

Sets the field's precision. This only affects numeric fields.

See also precision(), setType(), setRequiredStatus(), setLength(), setDefaultValue(), setGenerated(), and setReadOnly().

### QSqlField.setReadOnly (self, bool)

Sets the read only flag of the field's value to readOnly. A read-only field cannot have its value set with setValue() and cannot be cleared to NULL with clear().

See also isReadOnly().

### QSqlField.setRequired (self, bool)

Sets the required status of this field to Required if required is true; otherwise sets it to Optional.

See also setRequiredStatus() and requiredStatus().

### QSqlField.setRequiredStatus (self, RequiredStatus)

Sets the required status of this field to required.

See also requiredStatus(), setType(), setLength(), setPrecision(), setDefaultValue(), setGenerated(), and setReadOnly().

### QSqlField.setSqlType (self, int)

### QSqlField.setType (self, QVariant.Type)

Set's the field's variant type to type.

See also type(), setRequiredStatus(), setLength(), setPrecision(), setDefaultValue(), setGenerated(), and setReadOnly().

### QSqlField.setValue (self, QVariant)

Sets the value of the field to value. If the field is read-only (isReadOnly() returns true), nothing happens.

If the data type of value differs from the field's current data type, an attempt is made to cast it to the proper type. This preserves the data type of the field in the case of assignment, e.g. a QString to an integer data type.

To set the value to NULL, use clear().

See also value(), isReadOnly(), and defaultValue().

### QVariant.Type QSqlField.type (self)

Returns the field's type as stored in the database. Note that the actual value might have a different type, Numerical values that are too large to store in a long int or double are usually stored as strings to prevent precision loss.

See also setType().

### int QSqlField.typeID (self)

### QVariant QSqlField.value (self)

Returns the value of the field as a QVariant.

Use isNull() to check if the field's value is NULL.

See also setValue().

### bool QSqlField.__eq__ (self, QSqlField)

### bool QSqlField.__ne__ (self, QSqlField)