lockmodetype.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><!--NewPage--><HTML><HEAD><!-- Generated by javadoc (build 1.5.0_14) on Mon Jan 28 05:47:04 PST 2008 --><TITLE>LockModeType (Java EE 5)</TITLE><META NAME="keywords" CONTENT="javax.persistence.LockModeType class"><LINK REL ="stylesheet" TYPE="text/css" HREF="../../stylesheet.css" TITLE="Style"><SCRIPT type="text/javascript">function windowTitle(){ parent.document.title="LockModeType (Java EE 5)";}</SCRIPT><NOSCRIPT></NOSCRIPT></HEAD><BODY BGCOLOR="white" onload="windowTitle();"><!-- ========= START OF TOP NAVBAR ======= --><A NAME="navbar_top"><!-- --></A><A HREF="#skip-navbar_top" title="Skip navigation links"></A><TABLE BORDER="0" WIDTH="100%" CELLPADDING="1" CELLSPACING="0" SUMMARY=""><TR><TD COLSPAN=2 BGCOLOR="#EEEEFF" CLASS="NavBarCell1"><A NAME="navbar_top_firstrow"><!-- --></A><TABLE BORDER="0" CELLPADDING="0" CELLSPACING="3" SUMMARY=""> <TR ALIGN="center" VALIGN="top"> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../overview-summary.html"><FONT CLASS="NavBarFont1"><B>Overview</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-summary.html"><FONT CLASS="NavBarFont1"><B>Package</B></FONT></A> </TD> <TD BGCOLOR="#FFFFFF" CLASS="NavBarCell1Rev"> <FONT CLASS="NavBarFont1Rev"><B>Class</B></FONT> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-tree.html"><FONT CLASS="NavBarFont1"><B>Tree</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../deprecated-list.html"><FONT CLASS="NavBarFont1"><B>Deprecated</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../index-all.html"><FONT CLASS="NavBarFont1"><B>Index</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../help-doc.html"><FONT CLASS="NavBarFont1"><B>Help</B></FONT></A> </TD> </TR></TABLE></TD><TD ALIGN="right" VALIGN="top" ROWSPAN=3><EM></EM></TD></TR><TR><TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2"> <A HREF="../../javax/persistence/Lob.html" title="annotation in javax.persistence"><B>PREV CLASS</B></A> <A HREF="../../javax/persistence/ManyToMany.html" title="annotation in javax.persistence"><B>NEXT CLASS</B></A></FONT></TD><TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2"> <A HREF="../../index.html?javax/persistence/LockModeType.html" target="_top"><B>FRAMES</B></A> <A HREF="LockModeType.html" target="_top"><B>NO FRAMES</B></A> <SCRIPT type="text/javascript"> <!-- if(window==top) { document.writeln('<A HREF="../../allclasses-noframe.html"><B>All Classes</B></A>'); } //--></SCRIPT><NOSCRIPT> <A HREF="../../allclasses-noframe.html"><B>All Classes</B></A></NOSCRIPT></FONT></TD></TR><TR><TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2"> SUMMARY: NESTED | <A HREF="#enum_constant_summary">ENUM CONSTANTS</A> | FIELD | <A HREF="#method_summary">METHOD</A></FONT></TD><TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2">DETAIL: <A HREF="#enum_constant_detail">ENUM CONSTANTS</A> | FIELD | <A HREF="#method_detail">METHOD</A></FONT></TD></TR></TABLE><A NAME="skip-navbar_top"></A><!-- ========= END OF TOP NAVBAR ========= --><HR><!-- ======== START OF CLASS DATA ======== --><H2><FONT SIZE="-1">javax.persistence</FONT><BR>Enum LockModeType</H2><PRE><A HREF="http://java.sun.com/j2se/1.5/docs/api/java/lang/Object.html" title="class or interface in java.lang">java.lang.Object</A> <IMG SRC="../../resources/inherit.gif" ALT="extended by "><A HREF="http://java.sun.com/j2se/1.5/docs/api/java/lang/Enum.html" title="class or interface in java.lang">java.lang.Enum</A><<A HREF="../../javax/persistence/LockModeType.html" title="enum in javax.persistence">LockModeType</A>> <IMG SRC="../../resources/inherit.gif" ALT="extended by "><B>javax.persistence.LockModeType</B></PRE><DL><DT><B>All Implemented Interfaces:</B> <DD><A HREF="http://java.sun.com/j2se/1.5/docs/api/java/io/Serializable.html" title="class or interface in java.io">Serializable</A>, <A HREF="http://java.sun.com/j2se/1.5/docs/api/java/lang/Comparable.html" title="class or interface in java.lang">Comparable</A><<A HREF="../../javax/persistence/LockModeType.html" title="enum in javax.persistence">LockModeType</A>></DD></DL><HR><DL><DT><PRE>public enum <B>LockModeType</B><DT>extends <A HREF="http://java.sun.com/j2se/1.5/docs/api/java/lang/Enum.html" title="class or interface in java.lang">Enum</A><<A HREF="../../javax/persistence/LockModeType.html" title="enum in javax.persistence">LockModeType</A>></DL></PRE><P>Lock modes that can be specified by means of the <A HREF="../../javax/persistence/EntityManager.html#lock(java.lang.Object, javax.persistence.LockModeType)"><CODE>EntityManager.lock()</CODE></A> method. <p> The semantics of requesting locks of type <A HREF="../../javax/persistence/LockModeType.html#READ"><CODE>LockModeType.READ</CODE></A> and <A HREF="../../javax/persistence/LockModeType.html#WRITE"><CODE>LockModeType.WRITE</CODE></A> are the following. <p> If transaction T1 calls lock(entity, <A HREF="../../javax/persistence/LockModeType.html#READ"><CODE>LockModeType.READ</CODE></A>) on a versioned object, the entity manager must ensure that neither of the following phenomena can occur: <ul> <li> P1 (Dirty read): Transaction T1 modifies a row. Another transaction T2 then reads that row and obtains the modified value, before T1 has committed or rolled back. Transaction T2 eventually commits successfully; it does not matter whether T1 commits or rolls back and whether it does so before or after T2 commits. <li> </li> P2 (Non-repeatable read): Transaction T1 reads a row. Another transaction T2 then modifies or deletes that row, before T1 has committed. Both transactions eventually commit successfully. </li> </ul> <p> Lock modes must always prevent the phenomena P1 and P2. <p> In addition, calling lock(entity, LockModeType.WRITE) on a versioned object, will also force an update (increment) to the entity's version column. <p> The persistence implementation is not required to support calling <A HREF="../../javax/persistence/EntityManager.html#lock(java.lang.Object, javax.persistence.LockModeType)"><CODE>EntityManager.lock()</CODE></A> on a non-versioned object. When it cannot support a such lock call, it must throw the <A HREF="../../javax/persistence/PersistenceException.html" title="class in javax.persistence"><CODE>PersistenceException</CODE></A>.<P><P><DL><DT><B>Since:</B></DT> <DD>Java Persistence 1.0</DD></DL><HR><P><!-- =========== ENUM CONSTANT SUMMARY =========== --><A NAME="enum_constant_summary"><!-- --></A><TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY=""><TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"><TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2"><B>Enum Constant Summary</B></FONT></TH></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD><CODE><B><A HREF="../../javax/persistence/LockModeType.html#READ">READ</A></B></CODE><BR> Read lock</TD></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD><CODE><B><A HREF="../../javax/persistence/LockModeType.html#WRITE">WRITE</A></B></CODE><BR> Write lock</TD></TR></TABLE> <!-- ========== METHOD SUMMARY =========== --><A NAME="method_summary"><!-- --></A><TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY=""><TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"><TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2"><B>Method Summary</B></FONT></TH></TR><TR BGCOLOR="white" CLASS="TableRowColor"><TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"><CODE>static <A HREF="../../javax/persistence/LockModeType.html" title="enum in javax.persistence">LockModeType</A></CODE></FONT></TD><TD><CODE><B><A HREF="../../javax/persistence/LockModeType.html#valueOf(java.lang.String)">valueOf</A></B>(<A HREF="http://java.sun.com/j2se/1.5/docs/api/java/lang/String.html" title="class or interface in java.lang">String</A> name)</CODE>⌨️ 快捷键说明
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