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<HTML><HEAD><META http-equiv="Content-Type" content="text/html; charset=UTF-8"><TITLE>Perst.Query</TITLE><LINK REL=STYLESHEET HREF="../CommentReport.css" TYPE="text/css"></HEAD><BODY topmargin=0 rightmargin=0 leftmargin=0 style="background-image: url(../titletile.jpg); background-repeat:repeat-x; background-position: 0 0;" ><DIV CLASS="PageHeading">Perst.Query Interface</DIV><DIV CLASS="Description">
Class representing JSQL query. JSQL allows to select members of Perst collections
using SQL like predicate. Almost all Perst collections have select() method
which execute arbitrary JSQL query. But it is also possible to create Query instance explicitely,
Using storage.createQuery class. In this case it is possible to specify query with parameters,
once prepare query and then multiple times specify parameters and execute it.
Also Query interface allows to specify <i>indices</i> and <i>resolvers</i>.
JSQL can use arbitrary Perst <code>GenericIndex</code> to perform fast selection if object
instead of sequeial search. And user provided <i>resolver</i> allows to substitute SQL joins.
<P></DIV><IMG src="../GradLeft.jpg" width=7 height=378 alt="" border="0" style="position:absolute; left:10; top:18;z-Index:2"><IMG src="../GradTop.jpg" width=352 height=7 alt="" border="0" align="top" style="position:absolute; left:10; top:18; z-index:1"><DIV CLASS="Remarks"><SPAN CLASS="RemarkHdrX">Access: </SPAN>Public</DIV><TABLE CLASS="InfoTable" cellpadding=0 cellspacing=0><TR height=20><TD width=20> </TD><TD valign=top align=left width=9 bgcolor="#cccc66"><IMG SRC="../graycorner.jpg" align=top></TD><TD CLASS="TableLightLabel" WIDTH=206>Members</TD><TD CLASS="TableLightLabel" >Description</TD><TD width=20> </TD></TR><TR height=20><TD width=20> </TD><TD CLASS="TableLightDesc"> </TD><TD CLASS="TableLightDesc"><A HREF="CWP4103.HTM" TARGET="CNTFRAME">Select</A></TD><TD CLASS="TableLightDesc"> Execute query
<P></TD><TD width=20> </TD></TR><TR height=20><TD width=20> </TD><TD CLASS="TableLightDesc"> </TD><TD CLASS="TableLightDesc"><A HREF="CWP4104.HTM" TARGET="CNTFRAME">Select</A></TD><TD CLASS="TableLightDesc"> Execute query
<P></TD><TD width=20> </TD></TR><TR height=20><TD width=20> </TD><TD CLASS="TableLightDesc"> </TD><TD CLASS="TableLightDesc"><A HREF="CWP4105.HTM" TARGET="CNTFRAME">Prepare</A></TD><TD CLASS="TableLightDesc"> Prepare SQL statement
<P></TD><TD width=20> </TD></TR><TR height=20><TD width=20> </TD><TD CLASS="TableLightDesc"> </TD><TD CLASS="TableLightDesc"><A HREF="CWP4106.HTM" TARGET="CNTFRAME">Prepare</A></TD><TD CLASS="TableLightDesc"> Prepare SQL statement
<P></TD><TD width=20> </TD></TR><TR height=20><TD width=20> </TD><TD CLASS="TableLightDesc"> </TD><TD CLASS="TableLightDesc"><A HREF="CWP4107.HTM" TARGET="CNTFRAME">Execute</A></TD><TD CLASS="TableLightDesc"> Execute prepared query
<P></TD><TD width=20> </TD></TR><TR height=20><TD width=20> </TD><TD CLASS="TableLightDesc"> </TD><TD CLASS="TableLightDesc"><A HREF="CWP4108.HTM" TARGET="CNTFRAME">this</A></TD><TD CLASS="TableLightDesc">Set or get value of query parameter
<P></TD><TD width=20> </TD></TR><TR height=20><TD width=20> </TD><TD CLASS="TableLightDesc"> </TD><TD CLASS="TableLightDesc"><A HREF="CWP4110.HTM" TARGET="CNTFRAME">EnableRuntimeErrorReporting</A></TD><TD CLASS="TableLightDesc"> Enable or disable reporting of runtime errors on console.
Runtime errors during JSQL query are reported in two ways:
<OL>
<LI>If query error reporting is enabled then message is printed to System.err</LI>
<LI>If storage listener is registered, then JSQLRuntimeError of method listener is invoked</LI>
</OL>
By default reporting to System.err is enabled.
<P></TD><TD width=20> </TD></TR><TR height=20><TD width=20> </TD><TD CLASS="TableLightDesc"> </TD><TD CLASS="TableLightDesc"><A HREF="CWP4111.HTM" TARGET="CNTFRAME">SetResolver</A></TD><TD CLASS="TableLightDesc"> Specify resolver. Resolver can be used to replaced SQL JOINs: given object ID,
it will provide reference to the resolved object
<P></TD><TD width=20> </TD></TR><TR height=20><TD width=20> </TD><TD CLASS="TableLightDesc"> </TD><TD CLASS="TableLightDesc"><A HREF="CWP4112.HTM" TARGET="CNTFRAME">AddIndex</A></TD><TD CLASS="TableLightDesc"> Add index which can be used to optimize query execution (replace sequential search with direct index access)
<P></TD><TD width=20> </TD></TR></TABLE></BODY></HTML>⌨️ 快捷键说明
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