我在 QGIS 2.18 中使用 DB Manager 没有问题，但如果我尝试基于长时间运行的查询（1 分钟以上）添加图层，QGIS 将完全无法使用。似乎每次地图平移、每次鼠标点击等都会触发某种图层刷新。
这对一个人来说似乎很愚蠢，尤其是考虑到您可以右键单击图层并请求刷新。更重要的是，它使应用程序无法使用。我在这里做错了什么？是否无法创建图层并且仅在请求时更新？
显然我可以在 postgres 中为所有空间查询创建物化视图，但这似乎违背了在 QGIS 中能够做到这一点的意义
【问题讨论】：
不幸的是，repaintRequested() 信号没有触发刷新画布，所以我编写了一个小 Python 函数，您可以将其粘贴到 QGIS Python 控制台编辑器中，以从查询中生成物化视图并添加到 mapcanvas 作为动态图层添加用于根据需要刷新和重新加载视图的图例菜单操作
from qgis.core import QgsVectorLayer, QgsDataSourceURI, QgsMapLayerRegistry
from PyQt4.QtSql import QSqlDatabase
from PyQt4.QtGui import QAction
PSQLHost = "your_db_host"
PSQLPort = 5432
PSQLDatabase = "your_db"
PSQLUsername = "your_db_user"
PSQLPassword = "your_db_password"
LAYERNAME = "my materialized_view_layer"
QUERY = "select * from your_table"
class materialized_layer:
def __init__(self):
#setup connection
geom_field = "geom"
pkey_field = "id"
self.db = QSqlDatabase.addDatabase("QPSQL")
self.db.setHostName(PSQLHost)
self.db.setPort(PSQLPort)
self.db.setDatabaseName(PSQLDatabase)
self.db.setUserName(PSQLUsername)
self.db.setPassword(PSQLPassword)
self.db.open()
# generate materialized view
create_query = 'CREATE MATERIALIZED VIEW "%s" AS %s' % (LAYERNAME,QUERY)
self.db.exec_(create_query)
# add to canvas
qgis_uri = QgsDataSourceURI()
qgis_uri.setConnection(PSQLHost,str(PSQLPort),PSQLDatabase,PSQLUsername,PSQLPassword)
qgis_uri.setDataSource("",LAYERNAME,geom_field,"",pkey_field)
self.materialized_layer = QgsVectorLayer(qgis_uri.uri(), LAYERNAME, "postgres")
if self.materialized_layer.isValid():
#register new qgis layer and add action to layer contextual menu
QgsMapLayerRegistry.instance().addMapLayer(self.materialized_layer,True)
refresh_materialized_action = QAction( "Refresh materialized view and reload", iface.legendInterface() )
iface.legendInterface().addLegendLayerAction(refresh_materialized_action, "","", QgsMapLayer.VectorLayer,False)
iface.legendInterface().addLegendLayerActionForLayer(refresh_materialized_action, self.materialized_layer)
refresh_materialized_action.triggered.connect(self.refresh_layer)
else:
print "invalid layer"
def reload_layer(self):
print "RELOADING MATERIALIZED VIEW"
self.materialized_layer.reload()
def refresh_layer(self):
print "REFRESHING MATERIALIZED VIEW"
refresh_query = 'REFRESH MATERIALIZED VIEW "%s"' % LAYERNAME
self.db.exec_(refresh_query)
self.reload_layer()
l = materialized_layer ()
【讨论】：
我编写了一个名为postgisQueryBuilder 的插件，它有助于创建数据库视图，即使使用物化、指令和允许，浏览数据库连接可用层，以从 QGIS 刷新物化视图。 Check if you can be helpful.
【讨论】：