如何添加小部件以显示来自数据库的 SQLite 数据？

Question

很抱歉这篇文章的长度。 我尝试了大约 10 种不同的方法来解决我的问题，但都没有运气。 我想给出最可行的上下文。

我是 Pyqt5 的新手。 我正在制作一个联系人应用程序，我可以使用 pyqt5 GUI 应用程序将数据输入到 sqlite3 'contacts.db' 文件中。 我在应用程序的左侧有 GUI 输入字段。 我一直卡住的地方是如何在 GUI 应用程序右侧的显示框中显示“contacts.db”文件的内容？

这是一个屏幕截图：

到目前为止，这是我的代码：

import sys
from PyQt5 import  QtWidgets
from PyQt5.QtWidgets import QMainWindow,  QLabel, QLineEdit
from PyQt5.QtWidgets import QPushButton
from PyQt5.QtCore import QSize
from sqlite3 import *  

class MainWindow(QMainWindow):
    
    # Creating Main drop window
    def __init__(self):
        QMainWindow.__init__(self)
        
        # Sets dimentions for main drop window
        self.setMinimumSize(QSize(1000, 425)) 

        # Sets title for main drop window    
        self.setWindowTitle("Contacts") 
        
        def firstname():

            # Creates a label for first field
            self.nameLabel1 = QLabel(self)

            # Creates label text for first label
            self.nameLabel1.setText('First Name: ')

            # Creates first field
            self.line1 = QLineEdit(self)

            # Sets placement for first field
            self.line1.move(95, 50)

            # Sets size for first field
            self.line1.resize(200, 32)

            # Sets placement for first label
            self.nameLabel1.move(20, 50)

        firstname() 

        def lastname():
            self.nameLabel2 = QLabel(self)
            self.nameLabel2.setText('Last Name: ')
            self.line2 = QLineEdit(self)
            self.line2.move(95, 100)
            self.line2.resize(200, 32)
            self.nameLabel2.move(20, 100)
        lastname()

        def email():
            self.nameLabel3 = QLabel(self)
            self.nameLabel3.setText('Email: ')
            self.line3 = QLineEdit(self)
            self.line3.move(95, 150)
            self.line3.resize(200, 32)
            self.nameLabel3.move(20, 150)
        email()

        def phone():
            self.nameLabel4 = QLabel(self)
            self.nameLabel4.setText('Phone: ')
            self.line4 = QLineEdit(self)
            self.line4.move(95, 200)
            self.line4.resize(200, 32)
            self.nameLabel4.move(20, 200)
        phone()
        
        def phone():
            self.nameLabel5 = QLabel(self)
            self.nameLabel5.setText('Location: ')
            self.line5 = QLineEdit(self)
            self.line5.move(95, 250)
            self.line5.resize(200, 32)
            self.nameLabel5.move(20, 250)
        phone()
        
        def button():

            # Creates button, and button label
            pybutton1 = QPushButton('Add Contact', self)

            # Creates framwork for button funtion
            pybutton1.clicked.connect(self.clickMethod1)

            # Sets button size
            pybutton1.resize(200,32)

            # Sets button placement
            pybutton1.move(95, 325)   
        
        button()
    # Creates action that will be preformed when first button is pressed
    def clickMethod1(self):
        conn = connect('Contacts.db')
        c = conn.cursor()
        first = self.line1.text()
        last = self.line2.text()
        email = self.line3.text()
        phone = self.line4.text()
        loc = self.line5.text()

        c.execute(f"""INSERT INTO contacts VALUES('{first}',
        '{last}', '{email}', '{phone}', '{loc}')
        """)
    
        conn.commit()
        conn.close()

if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    mainWin = MainWindow()
    mainWin.show()
    sys.exit( app.exec_() )

要创建与我相同的数据库，您可以在 python 中运行它：

from sqlite3 import *

conn = connect('Contacts.db')
c = conn.cursor()

# Make table
def make():
    c.execute("""CREATE TABLE IF NOT EXISTS contacts(
    first TEXT,
    last TEXT,
    email TEXT,
    phone TEXT,
    location TEXT        
    )""")
make()

conn.commit()
conn.close()

非常感谢您的帮助！

Answer 1

Qt 已经通过QtSql模块提供了对 SQL 的支持，因此您通常不需要使用单独的 sql 模块进行通用使用。

使用model加载数据，并最终使用视图显示（阅读有关 Qt 的模型/视图编程范例的更多信息。

您基本上执行以下操作：

1. 加载数据库引擎；
2. select 一个数据库；
3. 创建一个 model （通常是QSqlTableModel ）；
4. 创建一个视图（通常是QTableView ）；
5. 使用setModel()为该视图设置 model ；

在以下示例中，您可以看到 model 已连接到数据库，并且由于直接对 model 进行了修改，因此表会随之自动更新。

^{请注意，我重新编写了您的代码，因为它有很多问题：首先，QMainWindow 应该始终有一个中央小部件，然后您还应该始终使用布局管理器而不是任意大小和位置； 我还删除了__init__中的函数，因为它们是不必要的，只会使代码分散注意力。}

from PyQt5 import QtCore, QtWidgets, QtSql

class MainWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super().__init__()
        central = QtWidgets.QWidget()
        mainLayout = QtWidgets.QGridLayout(central)
        mainLayout.setColumnStretch(0, 1)
        mainLayout.setColumnStretch(1, 2)

        formLayout = QtWidgets.QFormLayout()
        mainLayout.addLayout(formLayout, 0, 0)

        self.firstNameEdit = QtWidgets.QLineEdit()
        self.lastNameEdit = QtWidgets.QLineEdit()
        self.emailEdit = QtWidgets.QLineEdit()
        self.phoneEdit = QtWidgets.QLineEdit()
        self.locEdit = QtWidgets.QLineEdit()

        formLayout.addRow('First name:', self.firstNameEdit)
        formLayout.addRow('Last name:', self.lastNameEdit)
        formLayout.addRow('Email:', self.emailEdit)
        formLayout.addRow('Phone:', self.phoneEdit)
        formLayout.addRow('Location:', self.locEdit)

        self.addButton = QtWidgets.QPushButton('Add contact', enabled=False)
        mainLayout.addWidget(self.addButton, 1, 0)

        self.table = QtWidgets.QTableView()
        mainLayout.addWidget(self.table, 0, 1, 2, 1)
        self.table.setEditTriggers(self.table.NoEditTriggers)

        self.setCentralWidget(central)

        db = QtSql.QSqlDatabase.addDatabase('QSQLITE')
        db.setDatabaseName('Contacts.db')
        self.model = QtSql.QSqlTableModel()
        self.model.setTable('contacts')
        self.model.select()
        self.table.setModel(self.model)

        self.mandatoryFields = self.firstNameEdit, self.lastNameEdit
        self.otherFields = self.emailEdit, self.phoneEdit, self.locEdit
        self.allFields = self.mandatoryFields + self.otherFields

        for field in self.allFields:
            field.textChanged.connect(self.validate)

        self.addButton.clicked.connect(self.addRecord)

    def addRecord(self):
        record = self.model.record()
        for i, field in enumerate(self.allFields):
            record.setValue(i, field.text())
        row = self.model.rowCount()
        self.model.insertRow(row)
        self.model.setRecord(row, record)

    def validate(self):
        for field in self.mandatoryFields:
            if not field.text():
                self.addButton.setEnabled(False)
                return
        for field in self.otherFields:
            if field.text():
                break
        else:
            self.addButton.setEnabled(False)
            return
        self.addButton.setEnabled(True)

另请注意，Qt 提供了一个非常方便的 class， QDataWidgetMapper ，它允许将单个小部件与 model 的字段连接起来。 通过这种方式，您可以在用户选择索引时自动更新字段，或使用所有字段更新数据库。

这是上面代码的略微修改版本，实现了映射器（为简单起见，我再次发布整个代码，因为修改太复杂了）：

from PyQt5 import QtCore, QtWidgets, QtSql

class MainWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super().__init__()
        central = QtWidgets.QWidget()
        mainLayout = QtWidgets.QGridLayout(central)
        mainLayout.setColumnStretch(0, 1)
        mainLayout.setColumnStretch(1, 2)

        formLayout = QtWidgets.QFormLayout()
        mainLayout.addLayout(formLayout, 0, 0)

        self.firstNameEdit = QtWidgets.QLineEdit()
        self.lastNameEdit = QtWidgets.QLineEdit()
        self.emailEdit = QtWidgets.QLineEdit()
        self.phoneEdit = QtWidgets.QLineEdit()
        self.locEdit = QtWidgets.QLineEdit()

        formLayout.addRow('First name:', self.firstNameEdit)
        formLayout.addRow('Last name:', self.lastNameEdit)
        formLayout.addRow('Email:', self.emailEdit)
        formLayout.addRow('Phone:', self.phoneEdit)
        formLayout.addRow('Location:', self.locEdit)

        self.updateButton = QtWidgets.QPushButton('Update contact', enabled=False)
        self.addButton = QtWidgets.QPushButton('Add contact', enabled=False)
        buttonLayout = QtWidgets.QHBoxLayout()
        buttonLayout.addWidget(self.updateButton)
        buttonLayout.addWidget(self.addButton)
        mainLayout.addLayout(buttonLayout, 1, 0)

        self.table = QtWidgets.QTableView()
        mainLayout.addWidget(self.table, 0, 1, 2, 1)
        self.table.setEditTriggers(self.table.NoEditTriggers)

        self.setCentralWidget(central)

        db = QtSql.QSqlDatabase.addDatabase('QSQLITE')
        db.setDatabaseName('Contacts.db')
        self.model = QtSql.QSqlTableModel()
        self.model.setTable('contacts')
        self.model.select()
        self.table.setModel(self.model)
        self.table.setSelectionMode(self.table.SingleSelection)

        self.mandatoryFields = self.firstNameEdit, self.lastNameEdit
        self.otherFields = self.emailEdit, self.phoneEdit, self.locEdit
        self.allFields = self.mandatoryFields + self.otherFields

        self.mapper = QtWidgets.QDataWidgetMapper()
        self.mapper.setModel(self.model)
        self.mapper.setSubmitPolicy(self.mapper.ManualSubmit)

        for i, field in enumerate(self.allFields):
            field.textChanged.connect(self.validate)
            self.mapper.addMapping(field, i)

        self.addButton.clicked.connect(self.addRecord)
        self.updateButton.clicked.connect(self.updateRecord)
        self.table.selectionModel().selectionChanged.connect(self.selectionChanged)
        self.mapper.currentIndexChanged.connect(self.validate)
        self.table.doubleClicked.connect(self.doubleClicked)
        self.table.viewport().installEventFilter(self)

    def eventFilter(self, obj, event):
        if event.type() == event.MouseButtonPress:
            # clear all fields when clicking on an empty area of the table
            index = self.table.indexAt(event.pos())
            if not index.isValid():
                self.table.selectionModel().select(
                    index, QtCore.QItemSelectionModel.ClearAndSelect)
        return super().eventFilter(obj, event)

    def doubleClicked(self, index):
        widget = self.mapper.mappedWidgetAt(index.column())
        if widget:
            widget.setFocus()

    def selectedRow(self):
        selected = self.table.selectedIndexes()
        if selected:
            return selected[-1].row()
        return -1

    def selectionChanged(self):
        row = self.selectedRow()
        self.mapper.setCurrentIndex(row)
        if row < 0:
            for field in self.allFields:
                field.setText('')
        self.validate()

    def addRecord(self):
        # we cannot use submit(), as it will use the *current* index, nor we can
        # insert the new row and set the new index, as it would clear all fields
        record = self.model.record()
        for i, field in enumerate(self.allFields):
            record.setValue(i, field.text())
        row = self.model.rowCount()
        self.model.insertRow(row)
        self.model.setRecord(row, record)
        self.table.selectionModel().select(self.model.index(row, 0), 
            QtCore.QItemSelectionModel.ClearAndSelect)

    def updateRecord(self):
        row = self.selectedRow()
        if row < 0:
            self.updateButton.setEnabled(False)
            return
        self.mapper.submit()

    def validate(self):
        valid = True
        for field in self.mandatoryFields:
            if not field.text():
                valid = False
                break
        else:
            for field in self.otherFields:
                if field.text():
                    break
            else:
                valid = False
        self.addButton.setEnabled(valid)
        self.updateButton.setEnabled(valid and bool(self.table.selectedIndexes()))