1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>Chapter��3.��Direct Persistence Layer First Steps</title> 7 <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> 8 <meta name="generator" content="DocBook XSL Stylesheets V1.62.4" /> 9 <link rel="home" href="index.html" title="Getting Started with Berkeley DB" /> 10 <link rel="up" href="dpl.html" title="Part��I.��Programming with the Direct Persistence Layer" /> 11 <link rel="previous" href="dpl.html" title="Part��I.��Programming with the Direct Persistence Layer" /> 12 <link rel="next" href="persistobject.html" title="Persistent Objects" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">Chapter��3.��Direct Persistence Layer First Steps</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="dpl.html">Prev</a>��</td> 22 <th width="60%" align="center">Part��I.��Programming with the Direct Persistence Layer</th> 23 <td width="20%" align="right">��<a accesskey="n" href="persistobject.html">Next</a></td> 24 </tr> 25 </table> 26 <hr /> 27 </div> 28 <div class="chapter" lang="en" xml:lang="en"> 29 <div class="titlepage"> 30 <div> 31 <div> 32 <h2 class="title"><a id="persist_first"></a>Chapter��3.��Direct Persistence Layer First Steps</h2> 33 </div> 34 </div> 35 <div></div> 36 </div> 37 <div class="toc"> 38 <p> 39 <b>Table of Contents</b> 40 </p> 41 <dl> 42 <dt> 43 <span class="sect1"> 44 <a href="persist_first.html#entitystore">Entity Stores</a> 45 </span> 46 </dt> 47 <dd> 48 <dl> 49 <dt> 50 <span class="sect2"> 51 <a href="persist_first.html#persist-open">Opening and Closing Environments and Stores</a> 52 </span> 53 </dt> 54 </dl> 55 </dd> 56 <dt> 57 <span class="sect1"> 58 <a href="persistobject.html">Persistent Objects</a> 59 </span> 60 </dt> 61 <dt> 62 <span class="sect1"> 63 <a href="saveret.html">Saving a Retrieving Data</a> 64 </span> 65 </dt> 66 </dl> 67 </div> 68 <p> 69 This chapter guides you through the first few steps required to 70 use the DPL with your application. These steps include: 71 </p> 72 <div class="orderedlist"> 73 <ol type="1"> 74 <li> 75 <p> 76 Opening your environment as was described in 77 78 <span> 79 <a href="Env.html#EnvOpen">Opening Database Environments</a>. 80 </span> 81 </p> 82 </li> 83 <li> 84 <p> 85 Opening your entity store. 86 </p> 87 </li> 88 <li> 89 <p> 90 Identifying the classes that you want to store in 91 DB as either a <tt class="literal">persistent</tt> 92 class or an <tt class="literal">entity</tt>. 93 </p> 94 </li> 95 </ol> 96 </div> 97 <p> 98 Once you have done these things, you can write your classes to 99 the DB databases, read them back from the databases, delete 100 them from the databases, and so forth. These activities are 101 described in the chapters that follow in this part of this manual. 102 </p> 103 <div class="sect1" lang="en" xml:lang="en"> 104 <div class="titlepage"> 105 <div> 106 <div> 107 <h2 class="title" style="clear: both"><a id="entitystore"></a>Entity Stores</h2> 108 </div> 109 </div> 110 <div></div> 111 </div> 112 <p> 113 Entity stores are the basic unit of storage that you use with the DPL. That is, it 114 is a unit of encapsulation for the classes that you want to store in DB. Under 115 the hood it actually interacts with DB databases, but the DPL provides a layer 116 of abstraction from the underlying DB APIs. The store, therefore, provides a 117 simplified mechanism by which you read and write your stored classes. By using a 118 store, you have access to your classes that is more simplified than if you were 119 interacting with databases directly, but this simplified access comes at the cost of 120 reduced flexibility. 121 </p> 122 <p> 123 Entity stores have configurations in the same way that environments have 124 configurations. You can use a <tt class="classname">StoreConfig</tt> object 125 to identify store properties. Among these are methods that allow you to declare 126 whether: 127 </p> 128 <div class="itemizedlist"> 129 <ul type="disc"> 130 <li> 131 <p> 132 the store can be created if it does not exist at the time 133 it is opened. Use the 134 <tt class="methodname">StoreConfig.setAllowCreate()</tt> 135 method to set this. 136 </p> 137 </li> 138 <li> 139 <p> 140 deferred writes are allowed for the store. Use the 141 <tt class="methodname">StoreConfig.setDeferredWrite()</tt> 142 method to set this. 143 </p> 144 </li> 145 <li> 146 <p> 147 the store is read-only. Use the 148 <tt class="methodname">StoreConfig.setReadOnly()</tt> 149 method to set this. 150 </p> 151 </li> 152 <li> 153 <p> 154 the store supports transactions. Use the 155 <tt class="methodname">StoreConfig.setTransactional()</tt> 156 method to set this. 157 </p> 158 <p> 159 Writing DB transactional applications is described in the 160 <i class="citetitle">Berkeley DB Java Edition Getting Started with Transaction Processing</i> guide. 161 </p> 162 </li> 163 </ul> 164 </div> 165 <p> 166 <tt class="classname">EntityStore</tt> objects also provide methods for retrieving 167 information about the store, such as: 168 </p> 169 <div class="itemizedlist"> 170 <ul type="disc"> 171 <li> 172 <p> 173 the store's name. Use the 174 <tt class="methodname">EntityStore.getStoreName()</tt> 175 method to retrieve this. 176 </p> 177 </li> 178 <li> 179 <p> 180 a handle to the environment in which the store is opened. Use the 181 <tt class="methodname">EntityStore.getEnvironment</tt> 182 method to retrieve this handle. 183 </p> 184 </li> 185 </ul> 186 </div> 187 <p> 188 You can also use the <tt class="classname">EntityStore</tt> to 189 retrieve all the primary and secondary indexes related to a given type of entity 190 object contained in the store. See <a href="persist_index.html">Working with Indices</a> for 191 more information. 192 </p> 193 <div class="sect2" lang="en" xml:lang="en"> 194 <div class="titlepage"> 195 <div> 196 <div> 197 <h3 class="title"><a id="persist-open"></a>Opening and Closing Environments and Stores</h3> 198 </div> 199 </div> 200 <div></div> 201 </div> 202 <p> 203 As described in 204 205 <span> 206 <a href="Env.html">Database Environments</a>, 207 </span> 208 209 an 210 <span class="emphasis"><em>environment</em></span> is a unit of 211 encapsulation for DB databases. It also provides a 212 handle by which activities common across the databases 213 can be managed. 214 </p> 215 <p> 216 To use an entity store, you must first open an environment and then provide that 217 environment handle to the <tt class="classname">EntityStore</tt> constructor. 218 </p> 219 <p> 220 For example, the following code fragment configures both 221 the environment and the entity store such that they can 222 be created if they do not exist. Both the environment and 223 the entity store are then opened. 224 </p> 225 <pre class="programlisting">package persist.gettingStarted; 226 227import java.io.File; 228import java.io.FileNotFoundException; 229 230import com.sleepycat.db.DatabaseException; 231import com.sleepycat.db.Environment; 232import com.sleepycat.db.EnvironmentConfig; 233 234import com.sleepycat.persist.EntityStore; 235import com.sleepycat.persist.StoreConfig; 236 237... 238 239private Environment myEnv; 240private EntityStore store; 241 242try { 243 EnvironmentConfig myEnvConfig = new EnvironmentConfig(); 244 StoreConfig storeConfig = new StoreConfig(); 245 246 myEnvConfig.setAllowCreate(!readOnly); 247 storeConfig.setAllowCreate(!readOnly); 248 249 try { 250 // Open the environment and entity store 251 myEnv = new Environment(envHome, myEnvConfig); 252 store = new EntityStore(myEnv, "EntityStore", storeConfig); 253 } catch (FileNotFoundException fnfe) { 254 System.err.println(fnfe.toString()); 255 System.exit(-1); 256 } 257} catch(DatabaseException dbe) { 258 System.err.println("Error opening environment and store: " + 259 dbe.toString()); 260 System.exit(-1); 261} </pre> 262 <p> 263 As always, before you exit your program you should close both 264 your store and your environment. Be sure to close your store before you close your 265 environment. 266 </p> 267 <pre class="programlisting">if (store != null) { 268 try { 269 store.close(); 270 } catch(DatabaseException dbe) { 271 System.err.println("Error closing store: " + 272 dbe.toString()); 273 System.exit(-1); 274 } 275} 276 277if (myEnv != null) { 278 try { 279 // Finally, close environment. 280 myEnv.close(); 281 } catch(DatabaseException dbe) { 282 System.err.println("Error closing MyDbEnv: " + 283 dbe.toString()); 284 System.exit(-1); 285 } 286} </pre> 287 </div> 288 </div> 289 </div> 290 <div class="navfooter"> 291 <hr /> 292 <table width="100%" summary="Navigation footer"> 293 <tr> 294 <td width="40%" align="left"><a accesskey="p" href="dpl.html">Prev</a>��</td> 295 <td width="20%" align="center"> 296 <a accesskey="u" href="dpl.html">Up</a> 297 </td> 298 <td width="40%" align="right">��<a accesskey="n" href="persistobject.html">Next</a></td> 299 </tr> 300 <tr> 301 <td width="40%" align="left" valign="top">Part��I.��Programming with the Direct Persistence Layer��</td> 302 <td width="20%" align="center"> 303 <a accesskey="h" href="index.html">Home</a> 304 </td> 305 <td width="40%" align="right" valign="top">��Persistent Objects</td> 306 </tr> 307 </table> 308 </div> 309 </body> 310</html> 311