1 .. -*- coding: utf-8 -*- |
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2 |
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3 Frequently Asked Questions |
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4 ========================== |
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5 |
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6 [XXX 'copy answer from forum' means reusing text from |
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7 http://groups.google.com/group/google-appengine/browse_frm/thread/c9476925f5f66ec6 |
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8 and |
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9 http://groups.google.com/group/google-appengine/browse_frm/thread/d791ce17e2716147/eb078f8cfe8426e0 |
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10 and |
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11 http://groups.google.com/group/google-appengine/browse_frm/thread/f48cf6099973aef5/c28cd6934dd72457 |
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12 ] |
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13 |
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14 Why does not CubicWeb have a template language ? |
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15 ------------------------------------------------ |
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16 |
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17 There are enough template languages out there. You can use your |
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18 preferred template language if you want. [explain how to use a |
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19 template language] |
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20 |
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21 `CubicWeb` does not define its own templating language as this was |
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22 not our goal. Based on our experience, we realized that |
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23 we could gain productivity by letting designers use design tools |
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24 and developpers develop without the use of the templating language |
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25 as an intermediary that could not be anyway efficient for both parties. |
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26 Python is the templating language that we use in `CubicWeb`, but again, |
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27 it does not prevent you from using a templating language. |
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28 |
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29 The reason template languages are not used in this book is that |
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30 experience has proved us that using pure python was less cumbersome. |
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31 |
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32 Why do you think using pure python is better than using a template language ? |
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33 ----------------------------------------------------------------------------- |
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34 |
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35 Python is an Object Oriented Programming language and as such it |
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36 already provides a consistent and strong architecture and syntax |
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37 a templating language would not reach. |
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38 |
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39 When doing development, you need a real language and template |
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40 languages are not real languages. |
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41 |
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42 Using Python enables developing applications for which code is |
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43 easier to maintain with real functions/classes/contexts |
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44 without the need of learning a new dialect. By using Python, |
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45 we use standard OOP techniques and this is a key factor in a |
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46 robust application. |
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47 |
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48 Why do you use the GPL license to prevent me from doing X ? |
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49 ----------------------------------------------------------- |
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50 |
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51 GPL means that *if* you redistribute your application, you need to |
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52 redistribute it *and* the changes you made *and* the code _linked_ |
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53 to it under the GPL licence. |
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54 |
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55 Publishing a web site has nothing to do with redistributing |
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56 source code. A fair amount of companies use modified GPL code |
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57 for internal use. And someone could publish a `CubicWeb` component |
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58 under a BSD licence for others to plug into a GPL framework without |
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59 any problem. The only thing we are trying to prevent here is someone |
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60 taking the framework and packaging it as closed source to his own |
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61 clients. |
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62 |
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63 |
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64 CubicWeb looks pretty recent. Is it stable ? |
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65 -------------------------------------------- |
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66 |
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67 It is constantly evolving, piece by piece. The framework has |
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68 evolved over the past seven years and data has been migrated from |
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69 one schema to the other ever since. There is a well-defined way to |
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70 handle data and schema migration. |
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71 |
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72 Why is the RQL query language looking similar to X ? |
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73 ---------------------------------------------------- |
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74 |
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75 It may remind you of SQL but it is higher level than SQL, more like |
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76 SPARQL. Except that SPARQL did not exist when we started the project. |
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77 Having SPARQL has a query language has been in our backlog for years. |
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78 |
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79 That RQL language is what is going to make a difference with django- |
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80 like frameworks for several reasons. |
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81 |
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82 1. accessing data is *much* easier with it. One can write complex |
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83 queries with RQL that would be tedious to define and hard to maintain |
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84 using an object/filter suite of method calls. |
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85 |
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86 2. it offers an abstraction layer allowing your applications to run |
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87 on multiple back-ends. That means not only various SQL backends |
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88 (postgresql, sqlite, mysql), but also multiple databases at the |
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89 same time, and also non-SQL data stores like LDAP directories and |
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90 subversion/mercurial repositories (see the `vcsfile` |
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91 component). Google App Engine is yet another supported target for |
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92 RQL. |
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93 |
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94 [copy answer from forum, explain why similar to sparql and why better |
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95 than django and SQL] |
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96 |
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97 which ajax library |
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98 ------------------ |
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99 |
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100 [we use jquery and things on top of that] |
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101 |
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102 What is the CubicWeb datatype corresponding to GAE datastore's UserProperty? |
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103 ---------------------------------------------------------------------------- |
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104 |
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105 If you take a look at your application schema and |
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106 click on "display detailed view of metadata" you will see that there |
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107 is a Euser entity in there. That's the one that is modeling users. The |
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108 thing that corresponds to a UserProperty is a relationship between |
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109 your entity and the Euser entity. As in :: |
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110 |
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111 class TodoItem(EntityType): |
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112 text = String() |
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113 todo_by = SubjectRelation('Euser') |
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114 |
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115 [XXX check that cw handle users better by |
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116 mapping Google Accounts to local Euser entities automatically] |
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117 |
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118 |
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119 How to implement security? |
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120 -------------------------- |
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121 |
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122 This is an example of how it works in our framework:: |
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123 |
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124 class Version(EntityType): |
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125 """a version is defining the content of a particular project's |
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126 release""" |
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127 # definition of attributes is voluntarily missing |
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128 permissions = {'read': ('managers', 'users', 'guests',), |
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129 'update': ('managers', 'logilab', 'owners',), |
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130 'delete': ('managers', ), |
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131 'add': ('managers', 'logilab', |
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132 ERQLExpression('X version_of PROJ, U in_group G, PROJ |
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133 require_permission P, P name "add_version", P require_group G'),)} |
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134 |
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135 The above means that permission to read a Version is granted to any |
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136 user that is part of one of the groups 'managers', 'users', 'guests'. |
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137 The 'add' permission is granted to users in group 'managers' or |
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138 'logilab' and to users in group G, if G is linked by a permission |
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139 entity named "add_version" to the version's project. |
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140 :: |
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141 |
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142 class version_of(RelationType): |
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143 """link a version to its project. A version is necessarily linked |
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144 to one and only one project. """ |
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145 # some lines voluntarily missing |
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146 permissions = {'read': ('managers', 'users', 'guests',), |
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147 'delete': ('managers', ), |
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148 'add': ('managers', 'logilab', |
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149 RRQLExpression('O require_permission P, P name "add_version", |
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150 'U in_group G, P require_group G'),) } |
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151 |
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152 You can find additional information in the section :ref:`security`. |
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153 |
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154 [XXX what does the second example means in addition to the first one?] |
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155 |
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156 `Error while publishing rest text ...` |
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157 -------------------------------------- |
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158 |
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159 While modifying the description of an entity, you get an error message in |
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160 the application `Error while publishing ...` for Rest text and plain text. |
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161 The server returns a traceback like as follows :: |
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162 |
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163 2008-10-06 15:05:08 - (cubicweb.rest) ERROR: error while publishing ReST text |
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164 Traceback (most recent call last): |
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165 File "/home/user/src/blogdemo/cubicweb/common/rest.py", line 217, in rest_publish |
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166 File "/usr/lib/python2.5/codecs.py", line 817, in open |
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167 file = __builtin__.open(filename, mode, buffering) |
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168 TypeError: __init__() takes at most 3 arguments (4 given) |
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169 |
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170 |
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171 This can be fixed by applying the patch described in : |
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172 http://code.google.com/p/googleappengine/issues/detail?id=48 |
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173 |
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174 What are hooks used for? |
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175 ------------------------ |
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176 |
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177 Hooks are executed around (actually before or after) events. The |
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178 most common events are data creation, update and deletion. They |
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179 permit additional constraint checking (those not expressible at the |
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180 schema level), pre and post computations depending on data |
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181 movements. |
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182 |
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183 As such, they are a vital part of the framework. |
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184 |
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185 Other kinds of hooks, called Operations, are available |
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186 for execution just before commit. |
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187 |
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188 When should you define an HTML template rather than define a graphical component? |
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189 --------------------------------------------------------------------------------- |
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190 |
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191 An HTML template cannot contain code, hence it is only about static |
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192 content. A component is made of code and operations that apply on a |
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193 well defined context (request, result set). It enables much more |
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194 dynamic views. |
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195 |
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196 What is the difference between `AppRsetObject` and `AppObject` ? |
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197 ---------------------------------------------------------------- |
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198 |
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199 `AppRsetObject` instances are selected on a request and a result |
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200 set. `AppObject` instances are directly selected by id. |
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201 |
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202 How to update a database after a schema modification? |
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203 ----------------------------------------------------- |
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204 |
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205 It depends on what has been modified in the schema. |
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206 |
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207 * Update of an attribute permissions and properties: |
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208 ``synchronize_eschema('MyEntity')``. |
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209 |
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210 * Update of a relation permissions and properties: |
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211 ``synchronize_rschema('MyRelation')``. |
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212 |
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213 * Add an attribute: ``add_attribute('MyEntityType', 'myattr')``. |
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214 |
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215 * Add a relation: ``add_relation_definition('SubjRelation', 'MyRelation', 'ObjRelation')``. |
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216 |
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217 |
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218 How to create an anonymous user? |
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219 -------------------------------- |
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220 |
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221 This allows to bypass authentication for your site. In the |
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222 ``all-in-one.conf`` file of your instance, define the anonymous user |
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223 as follows :: |
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224 |
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225 # login of the CubicWeb user account to use for anonymous user (if you want to |
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226 # allow anonymous) |
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227 anonymous-user=anon |
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228 |
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229 # password of the CubicWeb user account matching login |
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230 anonymous-password=anon |
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231 |
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232 You also must ensure that this `anon` user is a registered user of |
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233 the DB backend. If not, you can create through the administation |
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234 interface of your instance by adding a user with the role `guests`. |
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235 This could be the admin account (for development |
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236 purposes, of course). |
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237 |
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238 .. note:: |
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239 While creating a new instance, you can decide to allow access |
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240 to anonymous user, which will automatically execute what is |
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241 decribed above. |
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242 |
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243 |
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244 How to change the application logo? |
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245 ----------------------------------- |
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246 |
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247 There are two ways of changing the logo. |
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248 |
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249 1. The easiest way to use a different logo is to replace the existing |
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250 ``logo.png`` in ``myapp/data`` by your prefered icon and refresh. |
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251 By default all application will look for a ``logo.png`` to be |
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252 rendered in the logo section. |
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253 |
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254 .. image:: images/lax-book.06-main-template-logo.en.png |
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255 |
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256 2. In your cube directory, you can specify which file to use for the logo. |
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257 This is configurable in ``mycube/data/external_resources``: :: |
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258 |
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259 LOGO = DATADIR/path/to/mylogo.gif |
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260 |
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261 where DATADIR is ``mycubes/data``. |
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262 |
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263 How to configure LDAP source? |
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264 ----------------------------- |
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265 |
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266 Your instance's sources are defined in ``/etc/cubicweb.d/myapp/sources``. |
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267 Configuring an LDAP source is about declaring that source in your |
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268 instance configuration file such as: :: |
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269 |
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270 [ldapuser] |
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271 adapter=ldapuser |
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272 # ldap host |
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273 host=myhost |
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274 # base DN to lookup for usres |
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275 user-base-dn=ou=People,dc=mydomain,dc=fr |
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276 # user search scope |
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277 user-scope=ONELEVEL |
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278 # classes of user |
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279 user-classes=top,posixAccount |
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280 # attribute used as login on authentication |
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281 user-login-attr=uid |
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282 # name of a group in which ldap users will be by default |
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283 user-default-group=users |
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284 # map from ldap user attributes to cubicweb attributes |
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285 user-attrs-map=gecos:email,uid:login |
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286 |
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287 Any change applied to configuration file requires to restart your |
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288 application. |
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289 |
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290 I get NoSelectableObject exceptions: how do I debug selectors ? |
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291 --------------------------------------------------------------- |
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292 |
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293 You just need to put the appropriate context manager around view/component |
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294 selection: :: |
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295 |
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296 from cubicweb.common.selectors import traced_selection |
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297 with traced_selection(): |
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298 comp = self.vreg.select_object('contentnavigation', 'wfhistory', |
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299 self.req, rset, context='navcontentbottom') |
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300 |
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301 This will yield additional WARNINGs, like this: :: |
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302 |
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303 2009-01-09 16:43:52 - (cubicweb.selectors) WARNING: selector one_line_rset returned 0 for <class 'cubicweb.web.views.basecomponents.WFHistoryVComponent'> |
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304 |
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305 How to format an entity date attribute? |
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306 --------------------------------------- |
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307 |
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308 If your schema has an attribute of type Date or Datetime, you might |
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309 want to format it. First, you should define your preferred format using |
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310 the site configuration panel ``http://appurl/view?vid=systemepropertiesform`` |
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311 and then set ``ui.date`` and/or ``ui.datetime``. |
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312 Then in the view code, use:: |
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313 |
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314 self.format_date(entity.date_attribute) |
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